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added in API level 26

Files

public final class Files
extends Object

java.lang.Object
   ↳ java.nio.file.Files


This class consists exclusively of static methods that operate on files, directories, or other types of files.

In most cases, the methods defined here will delegate to the associated file system provider to perform the file operations.

Summary

Public methods

static Path copy(Path source, Path target, CopyOption... options)

Copy a file to a target file.

static long copy(Path source, OutputStream out)

Copies all bytes from a file to an output stream.

static long copy(InputStream in, Path target, CopyOption... options)

Copies all bytes from an input stream to a file.

static Path createDirectories(Path dir, FileAttribute...<?> attrs)

Creates a directory by creating all nonexistent parent directories first.

static Path createDirectory(Path dir, FileAttribute...<?> attrs)

Creates a new directory.

static Path createFile(Path path, FileAttribute...<?> attrs)

Creates a new and empty file, failing if the file already exists.

static Path createLink(Path link, Path existing)

Creates a new link (directory entry) for an existing file (optional operation).

static Path createSymbolicLink(Path link, Path target, FileAttribute...<?> attrs)

Creates a symbolic link to a target (optional operation).

static Path createTempDirectory(String prefix, FileAttribute...<?> attrs)

Creates a new directory in the default temporary-file directory, using the given prefix to generate its name.

static Path createTempDirectory(Path dir, String prefix, FileAttribute...<?> attrs)

Creates a new directory in the specified directory, using the given prefix to generate its name.

static Path createTempFile(Path dir, String prefix, String suffix, FileAttribute...<?> attrs)

Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name.

static Path createTempFile(String prefix, String suffix, FileAttribute...<?> attrs)

Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name.

static void delete(Path path)

Deletes a file.

static boolean deleteIfExists(Path path)

Deletes a file if it exists.

static boolean exists(Path path, LinkOption... options)

Tests whether a file exists.

static Stream<Path> find(Path start, int maxDepth, BiPredicate<PathBasicFileAttributes> matcher, FileVisitOption... options)

Return a Stream that is lazily populated with Path by searching for files in a file tree rooted at a given starting file.

static Object getAttribute(Path path, String attribute, LinkOption... options)

Reads the value of a file attribute.

static <V extends FileAttributeView> V getFileAttributeView(Path path, Class<V> type, LinkOption... options)

Returns a file attribute view of a given type.

static FileStore getFileStore(Path path)

Returns the FileStore representing the file store where a file is located.

static FileTime getLastModifiedTime(Path path, LinkOption... options)

Returns a file's last modified time.

static UserPrincipal getOwner(Path path, LinkOption... options)

Returns the owner of a file.

static Set<PosixFilePermission> getPosixFilePermissions(Path path, LinkOption... options)

Returns a file's POSIX file permissions.

static boolean isDirectory(Path path, LinkOption... options)

Tests whether a file is a directory.

static boolean isExecutable(Path path)

Tests whether a file is executable.

static boolean isHidden(Path path)

Tells whether or not a file is considered hidden.

static boolean isReadable(Path path)

Tests whether a file is readable.

static boolean isRegularFile(Path path, LinkOption... options)

Tests whether a file is a regular file with opaque content.

static boolean isSameFile(Path path, Path path2)

Tests if two paths locate the same file.

static boolean isSymbolicLink(Path path)

Tests whether a file is a symbolic link.

static boolean isWritable(Path path)

Tests whether a file is writable.

static Stream<String> lines(Path path)

Read all lines from a file as a Stream.

static Stream<String> lines(Path path, Charset cs)

Read all lines from a file as a Stream.

static Stream<Path> list(Path dir)

Return a lazily populated Stream, the elements of which are the entries in the directory.

static Path move(Path source, Path target, CopyOption... options)

Move or rename a file to a target file.

static BufferedReader newBufferedReader(Path path, Charset cs)

Opens a file for reading, returning a BufferedReader that may be used to read text from the file in an efficient manner.

static BufferedReader newBufferedReader(Path path)

Opens a file for reading, returning a BufferedReader to read text from the file in an efficient manner.

static BufferedWriter newBufferedWriter(Path path, OpenOption... options)

Opens or creates a file for writing, returning a BufferedWriter to write text to the file in an efficient manner.

static BufferedWriter newBufferedWriter(Path path, Charset cs, OpenOption... options)

Opens or creates a file for writing, returning a BufferedWriter that may be used to write text to the file in an efficient manner.

static SeekableByteChannel newByteChannel(Path path, OpenOption... options)

Opens or creates a file, returning a seekable byte channel to access the file.

static SeekableByteChannel newByteChannel(Path path, Set<? extends OpenOption> options, FileAttribute...<?> attrs)

Opens or creates a file, returning a seekable byte channel to access the file.

static DirectoryStream<Path> newDirectoryStream(Path dir, String glob)

Opens a directory, returning a DirectoryStream to iterate over the entries in the directory.

static DirectoryStream<Path> newDirectoryStream(Path dir, Filter<? super Path> filter)

Opens a directory, returning a DirectoryStream to iterate over the entries in the directory.

static DirectoryStream<Path> newDirectoryStream(Path dir)

Opens a directory, returning a DirectoryStream to iterate over all entries in the directory.

static InputStream newInputStream(Path path, OpenOption... options)

Opens a file, returning an input stream to read from the file.

static OutputStream newOutputStream(Path path, OpenOption... options)

Opens or creates a file, returning an output stream that may be used to write bytes to the file.

static boolean notExists(Path path, LinkOption... options)

Tests whether the file located by this path does not exist.

static String probeContentType(Path path)

Probes the content type of a file.

static byte[] readAllBytes(Path path)

Reads all the bytes from a file.

static List<String> readAllLines(Path path, Charset cs)

Read all lines from a file.

static List<String> readAllLines(Path path)

Read all lines from a file.

static Map<StringObject> readAttributes(Path path, String attributes, LinkOption... options)

Reads a set of file attributes as a bulk operation.

static <A extends BasicFileAttributes> A readAttributes(Path path, Class<A> type, LinkOption... options)

Reads a file's attributes as a bulk operation.

static Path readSymbolicLink(Path link)

Reads the target of a symbolic link (optional operation).

static Path setAttribute(Path path, String attribute, Object value, LinkOption... options)

Sets the value of a file attribute.

static Path setLastModifiedTime(Path path, FileTime time)

Updates a file's last modified time attribute.

static Path setOwner(Path path, UserPrincipal owner)

Updates the file owner.

static Path setPosixFilePermissions(Path path, Set<PosixFilePermission> perms)

Sets a file's POSIX permissions.

static long size(Path path)

Returns the size of a file (in bytes).

static Stream<Path> walk(Path start, FileVisitOption... options)

Return a Stream that is lazily populated with Path by walking the file tree rooted at a given starting file.

static Stream<Path> walk(Path start, int maxDepth, FileVisitOption... options)

Return a Stream that is lazily populated with Path by walking the file tree rooted at a given starting file.

static Path walkFileTree(Path start, FileVisitor<? super Path> visitor)

Walks a file tree.

static Path walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor)

Walks a file tree.

static Path write(Path path, Iterable<? extends CharSequence> lines, OpenOption... options)

Write lines of text to a file.

static Path write(Path path, Iterable<? extends CharSequence> lines, Charset cs, OpenOption... options)

Write lines of text to a file.

static Path write(Path path, byte[] bytes, OpenOption... options)

Writes bytes to a file.

Inherited methods

Public methods

copy

added in API level 26
public static Path copy (Path source, 
                Path target, 
                CopyOption... options)

Copy a file to a target file.

This method copies a file to the target file with the options parameter specifying how the copy is performed. By default, the copy fails if the target file already exists or is a symbolic link, except if the source and target are the same file, in which case the method completes without copying the file. File attributes are not required to be copied to the target file. If symbolic links are supported, and the file is a symbolic link, then the final target of the link is copied. If the file is a directory then it creates an empty directory in the target location (entries in the directory are not copied). This method can be used with the walkFileTree method to copy a directory and all entries in the directory, or an entire file-tree where required.

The options parameter may include any of the following:

Option Description
REPLACE_EXISTING If the target file exists, then the target file is replaced if it is not a non-empty directory. If the target file exists and is a symbolic link, then the symbolic link itself, not the target of the link, is replaced.
COPY_ATTRIBUTES Attempts to copy the file attributes associated with this file to the target file. The exact file attributes that are copied is platform and file system dependent and therefore unspecified. Minimally, the last-modified-time is copied to the target file if supported by both the source and target file stores. Copying of file timestamps may result in precision loss.
NOFOLLOW_LINKS Symbolic links are not followed. If the file is a symbolic link, then the symbolic link itself, not the target of the link, is copied. It is implementation specific if file attributes can be copied to the new link. In other words, the COPY_ATTRIBUTES option may be ignored when copying a symbolic link.

An implementation of this interface may support additional implementation specific options.

Copying a file is not an atomic operation. If an IOException is thrown, then it is possible that the target file is incomplete or some of its file attributes have not been copied from the source file. When the REPLACE_EXISTING option is specified and the target file exists, then the target file is replaced. The check for the existence of the file and the creation of the new file may not be atomic with respect to other file system activities.

Usage Example: Suppose we want to copy a file into a directory, giving it the same file name as the source file:

     Path source = ...
     Path newdir = ...
     Files.copy(source, newdir.resolve(source.getFileName());
 

Parameters
source Path: the path to the file to copy

target Path: the path to the target file (may be associated with a different provider to the source path)

options CopyOption: options specifying how the copy should be done

Returns
Path the path to the target file

Throws
UnsupportedOperationException if the array contains a copy option that is not supported
FileAlreadyExistsException if the target file exists but cannot be replaced because the REPLACE_EXISTING option is not specified (optional specific exception)
DirectoryNotEmptyException the REPLACE_EXISTING option is specified but the file cannot be replaced because it is a non-empty directory (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the source file, the checkWrite is invoked to check write access to the target file. If a symbolic link is copied the security manager is invoked to check LinkPermission("symbolic").

copy

added in API level 26
public static long copy (Path source, 
                OutputStream out)

Copies all bytes from a file to an output stream.

If an I/O error occurs reading from the file or writing to the output stream, then it may do so after some bytes have been read or written. Consequently the output stream may be in an inconsistent state. It is strongly recommended that the output stream be promptly closed if an I/O error occurs.

This method may block indefinitely writing to the output stream (or reading from the file). The behavior for the case that the output stream is asynchronously closed or the thread interrupted during the copy is highly output stream and file system provider specific and therefore not specified.

Note that if the given output stream is Flushable then its flush method may need to invoked after this method completes so as to flush any buffered output.

Parameters
source Path: the path to the file

out OutputStream: the output stream to write to

Returns
long the number of bytes read or written

Throws
IOException if an I/O error occurs when reading or writing
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

copy

added in API level 26
public static long copy (InputStream in, 
                Path target, 
                CopyOption... options)

Copies all bytes from an input stream to a file. On return, the input stream will be at end of stream.

By default, the copy fails if the target file already exists or is a symbolic link. If the REPLACE_EXISTING option is specified, and the target file already exists, then it is replaced if it is not a non-empty directory. If the target file exists and is a symbolic link, then the symbolic link is replaced. In this release, the REPLACE_EXISTING option is the only option required to be supported by this method. Additional options may be supported in future releases.

If an I/O error occurs reading from the input stream or writing to the file, then it may do so after the target file has been created and after some bytes have been read or written. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the input stream be promptly closed if an I/O error occurs.

This method may block indefinitely reading from the input stream (or writing to the file). The behavior for the case that the input stream is asynchronously closed or the thread interrupted during the copy is highly input stream and file system provider specific and therefore not specified.

Usage example: Suppose we want to capture a web page and save it to a file:

     Path path = ...
     URI u = URI.create("http://java.sun.com/");
     try (InputStream in = u.toURL().openStream()) {
         Files.copy(in, path);
     }
 

Parameters
in InputStream: the input stream to read from

target Path: the path to the file

options CopyOption: options specifying how the copy should be done

Returns
long the number of bytes read or written

Throws
IOException if an I/O error occurs when reading or writing
FileAlreadyExistsException if the target file exists but cannot be replaced because the REPLACE_EXISTING option is not specified (optional specific exception)
DirectoryNotEmptyException the REPLACE_EXISTING option is specified but the file cannot be replaced because it is a non-empty directory (optional specific exception) *
UnsupportedOperationException if options contains a copy option that is not supported
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file. Where the REPLACE_EXISTING option is specified, the security manager's checkDelete method is invoked to check that an existing file can be deleted.

createDirectories

added in API level 26
public static Path createDirectories (Path dir, 
                FileAttribute...<?> attrs)

Creates a directory by creating all nonexistent parent directories first. Unlike the createDirectory method, an exception is not thrown if the directory could not be created because it already exists.

The attrs parameter is optional file-attributes to set atomically when creating the nonexistent directories. Each file attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

If this method fails, then it may do so after creating some, but not all, of the parent directories.

Parameters
dir Path: the directory to create

attrs FileAttribute: an optional list of file attributes to set atomically when creating the directory

Returns
Path the directory

Throws
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
FileAlreadyExistsException if dir exists but is not a directory (optional specific exception)
IOException if an I/O error occurs
SecurityException in the case of the default provider, and a security manager is installed, the checkWrite method is invoked prior to attempting to create a directory and its checkRead is invoked for each parent directory that is checked. If dir is not an absolute path then its toAbsolutePath may need to be invoked to get its absolute path. This may invoke the security manager's checkPropertyAccess method to check access to the system property user.dir

createDirectory

added in API level 26
public static Path createDirectory (Path dir, 
                FileAttribute...<?> attrs)

Creates a new directory. The check for the existence of the file and the creation of the directory if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the directory. The createDirectories method should be used where it is required to create all nonexistent parent directories first.

The attrs parameter is optional file-attributes to set atomically when creating the directory. Each attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

Parameters
dir Path: the directory to create

attrs FileAttribute: an optional list of file attributes to set atomically when creating the directory

Returns
Path the directory

Throws
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
FileAlreadyExistsException if a directory could not otherwise be created because a file of that name already exists (optional specific exception)
IOException if an I/O error occurs or the parent directory does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the new directory.

createFile

added in API level 26
public static Path createFile (Path path, 
                FileAttribute...<?> attrs)

Creates a new and empty file, failing if the file already exists. The check for the existence of the file and the creation of the new file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the directory.

The attrs parameter is optional file-attributes to set atomically when creating the file. Each attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

Parameters
path Path: the path to the file to create

attrs FileAttribute: an optional list of file attributes to set atomically when creating the file

Returns
Path the file

Throws
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the file
FileAlreadyExistsException if a file of that name already exists (optional specific exception)
IOException if an I/O error occurs or the parent directory does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the new file.

createLink

added in API level 26
public static Path createLink (Path link, 
                Path existing)

Creates a new link (directory entry) for an existing file (optional operation).

The link parameter locates the directory entry to create. The existing parameter is the path to an existing file. This method creates a new directory entry for the file so that it can be accessed using link as the path. On some file systems this is known as creating a "hard link". Whether the file attributes are maintained for the file or for each directory entry is file system specific and therefore not specified. Typically, a file system requires that all links (directory entries) for a file be on the same file system. Furthermore, on some platforms, the Java virtual machine may require to be started with implementation specific privileges to create hard links or to create links to directories.

Parameters
link Path: the link (directory entry) to create

existing Path: a path to an existing file

Returns
Path the path to the link (directory entry)

Throws
UnsupportedOperationException if the implementation does not support adding an existing file to a directory
FileAlreadyExistsException if the entry could not otherwise be created because a file of that name already exists (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it denies LinkPermission("hard") or its checkWrite method denies write access to either the link or the existing file.

createSymbolicLink

added in API level 26
public static Path createSymbolicLink (Path link, 
                Path target, 
                FileAttribute...<?> attrs)

Creates a symbolic link to a target (optional operation).

The target parameter is the target of the link. It may be an absolute or relative path and may not exist. When the target is a relative path then file system operations on the resulting link are relative to the path of the link.

The attrs parameter is optional attributes to set atomically when creating the link. Each attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

Where symbolic links are supported, but the underlying FileStore does not support symbolic links, then this may fail with an IOException. Additionally, some operating systems may require that the Java virtual machine be started with implementation specific privileges to create symbolic links, in which case this method may throw IOException.

Parameters
link Path: the path of the symbolic link to create

target Path: the target of the symbolic link

attrs FileAttribute: the array of attributes to set atomically when creating the symbolic link

Returns
Path the path to the symbolic link

Throws
UnsupportedOperationException if the implementation does not support symbolic links or the array contains an attribute that cannot be set atomically when creating the symbolic link
FileAlreadyExistsException if a file with the name already exists (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it denies LinkPermission("symbolic") or its checkWrite method denies write access to the path of the symbolic link.

createTempDirectory

added in API level 26
public static Path createTempDirectory (String prefix, 
                FileAttribute...<?> attrs)

Creates a new directory in the default temporary-file directory, using the given prefix to generate its name. The resulting Path is associated with the default FileSystem.

This method works in exactly the manner specified by createTempDirectory(Path, String, FileAttribute[]) method for the case that the dir parameter is the temporary-file directory.

Parameters
prefix String: the prefix string to be used in generating the directory's name; may be null

attrs FileAttribute: an optional list of file attributes to set atomically when creating the directory

Returns
Path the path to the newly created directory that did not exist before this method was invoked

Throws
IllegalArgumentException if the prefix cannot be used to generate a candidate directory name
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
IOException if an I/O error occurs or the temporary-file directory does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access when creating the directory.

createTempDirectory

added in API level 26
public static Path createTempDirectory (Path dir, 
                String prefix, 
                FileAttribute...<?> attrs)

Creates a new directory in the specified directory, using the given prefix to generate its name. The resulting Path is associated with the same FileSystem as the given directory.

The details as to how the name of the directory is constructed is implementation dependent and therefore not specified. Where possible the prefix is used to construct candidate names.

As with the createTempFile methods, this method is only part of a temporary-file facility. A shutdown-hook, or the File.deleteOnExit() mechanism may be used to delete the directory automatically.

The attrs parameter is optional file-attributes to set atomically when creating the directory. Each attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

Parameters
dir Path: the path to directory in which to create the directory

prefix String: the prefix string to be used in generating the directory's name; may be null

attrs FileAttribute: an optional list of file attributes to set atomically when creating the directory

Returns
Path the path to the newly created directory that did not exist before this method was invoked

Throws
IllegalArgumentException if the prefix cannot be used to generate a candidate directory name
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
IOException if an I/O error occurs or dir does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access when creating the directory.

createTempFile

added in API level 26
public static Path createTempFile (Path dir, 
                String prefix, 
                String suffix, 
                FileAttribute...<?> attrs)

Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name. The resulting Path is associated with the same FileSystem as the given directory.

The details as to how the name of the file is constructed is implementation dependent and therefore not specified. Where possible the prefix and suffix are used to construct candidate names in the same manner as the File.createTempFile(String, String, File) method.

As with the File.createTempFile methods, this method is only part of a temporary-file facility. Where used as a work files, the resulting file may be opened using the DELETE_ON_CLOSE option so that the file is deleted when the appropriate close method is invoked. Alternatively, a shutdown-hook, or the File.deleteOnExit() mechanism may be used to delete the file automatically.

The attrs parameter is optional file-attributes to set atomically when creating the file. Each attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored. When no file attributes are specified, then the resulting file may have more restrictive access permissions to files created by the File.createTempFile(String, String, File) method.

Parameters
dir Path: the path to directory in which to create the file

prefix String: the prefix string to be used in generating the file's name; may be null

suffix String: the suffix string to be used in generating the file's name; may be null, in which case ".tmp" is used

attrs FileAttribute: an optional list of file attributes to set atomically when creating the file

Returns
Path the path to the newly created file that did not exist before this method was invoked

Throws
IllegalArgumentException if the prefix or suffix parameters cannot be used to generate a candidate file name
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
IOException if an I/O error occurs or dir does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

createTempFile

added in API level 26
public static Path createTempFile (String prefix, 
                String suffix, 
                FileAttribute...<?> attrs)

Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name. The resulting Path is associated with the default FileSystem.

This method works in exactly the manner specified by the createTempFile(Path, String, String, FileAttribute[]) method for the case that the dir parameter is the temporary-file directory.

Parameters
prefix String: the prefix string to be used in generating the file's name; may be null

suffix String: the suffix string to be used in generating the file's name; may be null, in which case ".tmp" is used

attrs FileAttribute: an optional list of file attributes to set atomically when creating the file

Returns
Path the path to the newly created file that did not exist before this method was invoked

Throws
IllegalArgumentException if the prefix or suffix parameters cannot be used to generate a candidate file name
UnsupportedOperationException if the array contains an attribute that cannot be set atomically when creating the directory
IOException if an I/O error occurs or the temporary-file directory does not exist
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

delete

added in API level 26
public static void delete (Path path)

Deletes a file.

An implementation may require to examine the file to determine if the file is a directory. Consequently this method may not be atomic with respect to other file system operations. If the file is a symbolic link then the symbolic link itself, not the final target of the link, is deleted.

If the file is a directory then the directory must be empty. In some implementations a directory has entries for special files or links that are created when the directory is created. In such implementations a directory is considered empty when only the special entries exist. This method can be used with the walkFileTree method to delete a directory and all entries in the directory, or an entire file-tree where required.

On some operating systems it may not be possible to remove a file when it is open and in use by this Java virtual machine or other programs.

Parameters
path Path: the path to the file to delete

Throws
NoSuchFileException if the file does not exist (optional specific exception)
DirectoryNotEmptyException if the file is a directory and could not otherwise be deleted because the directory is not empty (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the SecurityManager.checkDelete(String) method is invoked to check delete access to the file

deleteIfExists

added in API level 26
public static boolean deleteIfExists (Path path)

Deletes a file if it exists.

As with the delete(Path) method, an implementation may need to examine the file to determine if the file is a directory. Consequently this method may not be atomic with respect to other file system operations. If the file is a symbolic link, then the symbolic link itself, not the final target of the link, is deleted.

If the file is a directory then the directory must be empty. In some implementations a directory has entries for special files or links that are created when the directory is created. In such implementations a directory is considered empty when only the special entries exist.

On some operating systems it may not be possible to remove a file when it is open and in use by this Java virtual machine or other programs.

Parameters
path Path: the path to the file to delete

Returns
boolean true if the file was deleted by this method; false if the file could not be deleted because it did not exist

Throws
DirectoryNotEmptyException if the file is a directory and could not otherwise be deleted because the directory is not empty (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the SecurityManager.checkDelete(String) method is invoked to check delete access to the file.

exists

added in API level 26
public static boolean exists (Path path, 
                LinkOption... options)

Tests whether a file exists.

The options parameter may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Note that the result of this method is immediately outdated. If this method indicates the file exists then there is no guarantee that a subsequence access will succeed. Care should be taken when using this method in security sensitive applications.

Parameters
path Path: the path to the file to test

options LinkOption: options indicating how symbolic links are handled .

Returns
boolean true if the file exists; false if the file does not exist or its existence cannot be determined.

Throws
SecurityException In the case of the default provider, the SecurityManager.checkRead(String) is invoked to check read access to the file.

find

added in API level 26
public static Stream<Path> find (Path start, 
                int maxDepth, 
                BiPredicate<PathBasicFileAttributes> matcher, 
                FileVisitOption... options)

Return a Stream that is lazily populated with Path by searching for files in a file tree rooted at a given starting file.

This method walks the file tree in exactly the manner specified by the walk method. For each file encountered, the given BiPredicate is invoked with its Path and BasicFileAttributes. The Path object is obtained as if by resolving the relative path against start and is only included in the returned Stream if the BiPredicate returns true. Compare to calling filter on the Stream returned by walk method, this method may be more efficient by avoiding redundant retrieval of the BasicFileAttributes.

The returned stream encapsulates one or more DirectoryStreams. If timely disposal of file system resources is required, the try-with-resources construct should be used to ensure that the stream's close method is invoked after the stream operations are completed. Operating on a closed stream will result in an IllegalStateException.

If an IOException is thrown when accessing the directory after returned from this method, it is wrapped in an UncheckedIOException which will be thrown from the method that caused the access to take place.

Parameters
start Path: the starting file

maxDepth int: the maximum number of directory levels to search

matcher BiPredicate: the function used to decide whether a file should be included in the returned stream

options FileVisitOption: options to configure the traversal

Returns
Stream<Path> the Stream of Path

Throws
IllegalArgumentException if the maxDepth parameter is negative
SecurityException If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.
IOException if an I/O error is thrown when accessing the starting file.

getAttribute

added in API level 26
public static Object getAttribute (Path path, 
                String attribute, 
                LinkOption... options)

Reads the value of a file attribute.

The attribute parameter identifies the attribute to be read and takes the form:

[view-name:]attribute-name
where square brackets [...] delineate an optional component and the character ':' stands for itself.

view-name is the name of a FileAttributeView that identifies a set of file attributes. If not specified then it defaults to "basic", the name of the file attribute view that identifies the basic set of file attributes common to many file systems. attribute-name is the name of the attribute.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Usage Example: Suppose we require the user ID of the file owner on a system that supports a "unix" view:

    Path path = ...
    int uid = (Integer)Files.getAttribute(path, "unix:uid");
 

Parameters
path Path: the path to the file

attribute String: the attribute to read

options LinkOption: options indicating how symbolic links are handled

Returns
Object the attribute value

Throws
UnsupportedOperationException if the attribute view is not available
IllegalArgumentException if the attribute name is not specified or is not recognized
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file. If this method is invoked to read security sensitive attributes then the security manager may be invoked to check for additional permissions.

getFileAttributeView

added in API level 26
public static V getFileAttributeView (Path path, 
                Class<V> type, 
                LinkOption... options)

Returns a file attribute view of a given type.

A file attribute view provides a read-only or updatable view of a set of file attributes. This method is intended to be used where the file attribute view defines type-safe methods to read or update the file attributes. The type parameter is the type of the attribute view required and the method returns an instance of that type if supported. The BasicFileAttributeView type supports access to the basic attributes of a file. Invoking this method to select a file attribute view of that type will always return an instance of that class.

The options array may be used to indicate how symbolic links are handled by the resulting file attribute view for the case that the file is a symbolic link. By default, symbolic links are followed. If the option NOFOLLOW_LINKS is present then symbolic links are not followed. This option is ignored by implementations that do not support symbolic links.

Usage Example: Suppose we want read or set a file's ACL, if supported:

     Path path = ...
     AclFileAttributeView view = Files.getFileAttributeView(path, AclFileAttributeView.class);
     if (view != null) {
         List<AclEntry> acl = view.getAcl();
         :
     }
 

Parameters
path Path: the path to the file

type Class: the Class object corresponding to the file attribute view

options LinkOption: options indicating how symbolic links are handled

Returns
V a file attribute view of the specified type, or null if the attribute view type is not available

getFileStore

added in API level 26
public static FileStore getFileStore (Path path)

Returns the FileStore representing the file store where a file is located.

Once a reference to the FileStore is obtained it is implementation specific if operations on the returned FileStore, or FileStoreAttributeView objects obtained from it, continue to depend on the existence of the file. In particular the behavior is not defined for the case that the file is deleted or moved to a different file store.

Parameters
path Path: the path to the file

Returns
FileStore the file store where the file is stored

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file, and in addition it checks RuntimePermission ("getFileStoreAttributes")

getLastModifiedTime

added in API level 26
public static FileTime getLastModifiedTime (Path path, 
                LinkOption... options)

Returns a file's last modified time.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Parameters
path Path: the path to the file

options LinkOption: options indicating how symbolic links are handled

Returns
FileTime a FileTime representing the time the file was last modified, or an implementation specific default when a time stamp to indicate the time of last modification is not supported by the file system

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file.

getOwner

added in API level 26
public static UserPrincipal getOwner (Path path, 
                LinkOption... options)

Returns the owner of a file.

The path parameter is associated with a file system that supports FileOwnerAttributeView. This file attribute view provides access to a file attribute that is the owner of the file.

Parameters
path Path: The path to the file

options LinkOption: options indicating how symbolic links are handled

Returns
UserPrincipal A user principal representing the owner of the file

Throws
UnsupportedOperationException if the associated file system does not support the FileOwnerAttributeView
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it denies RuntimePermission("accessUserInformation") or its checkRead method denies read access to the file.

getPosixFilePermissions

added in API level 26
public static Set<PosixFilePermission> getPosixFilePermissions (Path path, 
                LinkOption... options)

Returns a file's POSIX file permissions.

The path parameter is associated with a FileSystem that supports the PosixFileAttributeView. This attribute view provides access to file attributes commonly associated with files on file systems used by operating systems that implement the Portable Operating System Interface (POSIX) family of standards.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Parameters
path Path: the path to the file

options LinkOption: options indicating how symbolic links are handled

Returns
Set<PosixFilePermission> the file permissions

Throws
UnsupportedOperationException if the associated file system does not support the PosixFileAttributeView
IOException if an I/O error occurs
SecurityException In the case of the default provider, a security manager is installed, and it denies RuntimePermission("accessUserInformation") or its checkRead method denies read access to the file.

isDirectory

added in API level 26
public static boolean isDirectory (Path path, 
                LinkOption... options)

Tests whether a file is a directory.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Where it is required to distinguish an I/O exception from the case that the file is not a directory then the file attributes can be read with the readAttributes method and the file type tested with the BasicFileAttributes.isDirectory() method.

Parameters
path Path: the path to the file to test

options LinkOption: options indicating how symbolic links are handled

Returns
boolean true if the file is a directory; false if the file does not exist, is not a directory, or it cannot be determined if the file is a directory or not.

Throws
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file.

isExecutable

added in API level 26
public static boolean isExecutable (Path path)

Tests whether a file is executable. This method checks that a file exists and that this Java virtual machine has appropriate privileges to execute the file. The semantics may differ when checking access to a directory. For example, on UNIX systems, checking for execute access checks that the Java virtual machine has permission to search the directory in order to access file or subdirectories.

Depending on the implementation, this method may require to read file permissions, access control lists, or other file attributes in order to check the effective access to the file. Consequently, this method may not be atomic with respect to other file system operations.

Note that the result of this method is immediately outdated, there is no guarantee that a subsequent attempt to execute the file will succeed (or even that it will access the same file). Care should be taken when using this method in security sensitive applications.

Parameters
path Path: the path to the file to check

Returns
boolean true if the file exists and is executable; false if the file does not exist, execute access would be denied because the Java virtual machine has insufficient privileges, or access cannot be determined

Throws
SecurityException In the case of the default provider, and a security manager is installed, the checkExec is invoked to check execute access to the file.

isHidden

added in API level 26
public static boolean isHidden (Path path)

Tells whether or not a file is considered hidden. The exact definition of hidden is platform or provider dependent. On UNIX for example a file is considered to be hidden if its name begins with a period character ('.'). On Windows a file is considered hidden if it isn't a directory and the DOS hidden attribute is set.

Depending on the implementation this method may require to access the file system to determine if the file is considered hidden.

Parameters
path Path: the path to the file to test

Returns
boolean true if the file is considered hidden

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

isReadable

added in API level 26
public static boolean isReadable (Path path)

Tests whether a file is readable. This method checks that a file exists and that this Java virtual machine has appropriate privileges that would allow it open the file for reading. Depending on the implementation, this method may require to read file permissions, access control lists, or other file attributes in order to check the effective access to the file. Consequently, this method may not be atomic with respect to other file system operations.

Note that the result of this method is immediately outdated, there is no guarantee that a subsequent attempt to open the file for reading will succeed (or even that it will access the same file). Care should be taken when using this method in security sensitive applications.

Parameters
path Path: the path to the file to check

Returns
boolean true if the file exists and is readable; false if the file does not exist, read access would be denied because the Java virtual machine has insufficient privileges, or access cannot be determined

Throws
SecurityException In the case of the default provider, and a security manager is installed, the checkRead is invoked to check read access to the file.

isRegularFile

added in API level 26
public static boolean isRegularFile (Path path, 
                LinkOption... options)

Tests whether a file is a regular file with opaque content.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Where it is required to distinguish an I/O exception from the case that the file is not a regular file then the file attributes can be read with the readAttributes method and the file type tested with the BasicFileAttributes.isRegularFile() method.

Parameters
path Path: the path to the file

options LinkOption: options indicating how symbolic links are handled

Returns
boolean true if the file is a regular file; false if the file does not exist, is not a regular file, or it cannot be determined if the file is a regular file or not.

Throws
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file.

isSameFile

added in API level 26
public static boolean isSameFile (Path path, 
                Path path2)

Tests if two paths locate the same file.

If both Path objects are equal then this method returns true without checking if the file exists. If the two Path objects are associated with different providers then this method returns false. Otherwise, this method checks if both Path objects locate the same file, and depending on the implementation, may require to open or access both files.

If the file system and files remain static, then this method implements an equivalence relation for non-null Paths.

  • It is reflexive: for Path f, isSameFile(f,f) should return true.
  • It is symmetric: for two Paths f and g, isSameFile(f,g) will equal isSameFile(g,f).
  • It is transitive: for three Paths f, g, and h, if isSameFile(f,g) returns true and isSameFile(g,h) returns true, then isSameFile(f,h) will return return true.

Parameters
path Path: one path to the file

path2 Path: the other path

Returns
boolean true if, and only if, the two paths locate the same file

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to both files.

isSymbolicLink

added in API level 26
public static boolean isSymbolicLink (Path path)

Tests whether a file is a symbolic link.

Where it is required to distinguish an I/O exception from the case that the file is not a symbolic link then the file attributes can be read with the readAttributes method and the file type tested with the BasicFileAttributes.isSymbolicLink() method.

Parameters
path Path: The path to the file

Returns
boolean true if the file is a symbolic link; false if the file does not exist, is not a symbolic link, or it cannot be determined if the file is a symbolic link or not.

Throws
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file.

isWritable

added in API level 26
public static boolean isWritable (Path path)

Tests whether a file is writable. This method checks that a file exists and that this Java virtual machine has appropriate privileges that would allow it open the file for writing. Depending on the implementation, this method may require to read file permissions, access control lists, or other file attributes in order to check the effective access to the file. Consequently, this method may not be atomic with respect to other file system operations.

Note that result of this method is immediately outdated, there is no guarantee that a subsequent attempt to open the file for writing will succeed (or even that it will access the same file). Care should be taken when using this method in security sensitive applications.

Parameters
path Path: the path to the file to check

Returns
boolean true if the file exists and is writable; false if the file does not exist, write access would be denied because the Java virtual machine has insufficient privileges, or access cannot be determined

Throws
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite is invoked to check write access to the file.

lines

added in API level 26
public static Stream<String> lines (Path path)

Read all lines from a file as a Stream. Bytes from the file are decoded into characters using the UTF-8 charset.

This method works as if invoking it were equivalent to evaluating the expression:

Files.lines(path, StandardCharsets.UTF_8)
 

Parameters
path Path: the path to the file

Returns
Stream<String> the lines from the file as a Stream

Throws
IOException if an I/O error occurs opening the file
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

lines

added in API level 26
public static Stream<String> lines (Path path, 
                Charset cs)

Read all lines from a file as a Stream. Unlike readAllLines, this method does not read all lines into a List, but instead populates lazily as the stream is consumed.

Bytes from the file are decoded into characters using the specified charset and the same line terminators as specified by readAllLines are supported.

After this method returns, then any subsequent I/O exception that occurs while reading from the file or when a malformed or unmappable byte sequence is read, is wrapped in an UncheckedIOException that will be thrown from the Stream method that caused the read to take place. In case an IOException is thrown when closing the file, it is also wrapped as an UncheckedIOException.

The returned stream encapsulates a Reader. If timely disposal of file system resources is required, the try-with-resources construct should be used to ensure that the stream's close method is invoked after the stream operations are completed.

Parameters
path Path: the path to the file

cs Charset: the charset to use for decoding

Returns
Stream<String> the lines from the file as a Stream

Throws
IOException if an I/O error occurs opening the file
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

list

added in API level 26
public static Stream<Path> list (Path dir)

Return a lazily populated Stream, the elements of which are the entries in the directory. The listing is not recursive.

The elements of the stream are Path objects that are obtained as if by resolving the name of the directory entry against dir. Some file systems maintain special links to the directory itself and the directory's parent directory. Entries representing these links are not included.

The stream is weakly consistent. It is thread safe but does not freeze the directory while iterating, so it may (or may not) reflect updates to the directory that occur after returning from this method.

The returned stream encapsulates a DirectoryStream. If timely disposal of file system resources is required, the try-with-resources construct should be used to ensure that the stream's close method is invoked after the stream operations are completed.

Operating on a closed stream behaves as if the end of stream has been reached. Due to read-ahead, one or more elements may be returned after the stream has been closed.

If an IOException is thrown when accessing the directory after this method has returned, it is wrapped in an UncheckedIOException which will be thrown from the method that caused the access to take place.

Parameters
dir Path: The path to the directory

Returns
Stream<Path> The Stream describing the content of the directory

Throws
NotDirectoryException if the file could not otherwise be opened because it is not a directory (optional specific exception)
IOException if an I/O error occurs when opening the directory
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the directory.

move

added in API level 26
public static Path move (Path source, 
                Path target, 
                CopyOption... options)

Move or rename a file to a target file.

By default, this method attempts to move the file to the target file, failing if the target file exists except if the source and target are the same file, in which case this method has no effect. If the file is a symbolic link then the symbolic link itself, not the target of the link, is moved. This method may be invoked to move an empty directory. In some implementations a directory has entries for special files or links that are created when the directory is created. In such implementations a directory is considered empty when only the special entries exist. When invoked to move a directory that is not empty then the directory is moved if it does not require moving the entries in the directory. For example, renaming a directory on the same FileStore will usually not require moving the entries in the directory. When moving a directory requires that its entries be moved then this method fails (by throwing an IOException). To move a file tree may involve copying rather than moving directories and this can be done using the copy method in conjunction with the Files.walkFileTree utility method.

The options parameter may include any of the following:

Option Description
REPLACE_EXISTING If the target file exists, then the target file is replaced if it is not a non-empty directory. If the target file exists and is a symbolic link, then the symbolic link itself, not the target of the link, is replaced.
ATOMIC_MOVE The move is performed as an atomic file system operation and all other options are ignored. If the target file exists then it is implementation specific if the existing file is replaced or this method fails by throwing an IOException. If the move cannot be performed as an atomic file system operation then AtomicMoveNotSupportedException is thrown. This can arise, for example, when the target location is on a different FileStore and would require that the file be copied, or target location is associated with a different provider to this object.

An implementation of this interface may support additional implementation specific options.

Moving a file will copy the last-modified-time to the target file if supported by both source and target file stores. Copying of file timestamps may result in precision loss. An implementation may also attempt to copy other file attributes but is not required to fail if the file attributes cannot be copied. When the move is performed as a non-atomic operation, and an IOException is thrown, then the state of the files is not defined. The original file and the target file may both exist, the target file may be incomplete or some of its file attributes may not been copied from the original file.

Usage Examples: Suppose we want to rename a file to "newname", keeping the file in the same directory:

     Path source = ...
     Files.move(source, source.resolveSibling("newname"));
 
Alternatively, suppose we want to move a file to new directory, keeping the same file name, and replacing any existing file of that name in the directory:
     Path source = ...
     Path newdir = ...
     Files.move(source, newdir.resolve(source.getFileName()), REPLACE_EXISTING);
 

Parameters
source Path: the path to the file to move

target Path: the path to the target file (may be associated with a different provider to the source path)

options CopyOption: options specifying how the move should be done

Returns
Path the path to the target file

Throws
UnsupportedOperationException if the array contains a copy option that is not supported
FileAlreadyExistsException if the target file exists but cannot be replaced because the REPLACE_EXISTING option is not specified (optional specific exception)
DirectoryNotEmptyException the REPLACE_EXISTING option is specified but the file cannot be replaced because it is a non-empty directory (optional specific exception)
AtomicMoveNotSupportedException if the options array contains the ATOMIC_MOVE option but the file cannot be moved as an atomic file system operation.
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to both the source and target file.

newBufferedReader

added in API level 26
public static BufferedReader newBufferedReader (Path path, 
                Charset cs)

Opens a file for reading, returning a BufferedReader that may be used to read text from the file in an efficient manner. Bytes from the file are decoded into characters using the specified charset. Reading commences at the beginning of the file.

The Reader methods that read from the file throw IOException if a malformed or unmappable byte sequence is read.

Parameters
path Path: the path to the file

cs Charset: the charset to use for decoding

Returns
BufferedReader a new buffered reader, with default buffer size, to read text from the file

Throws
IOException if an I/O error occurs opening the file
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

See also:

newBufferedReader

added in API level 26
public static BufferedReader newBufferedReader (Path path)

Opens a file for reading, returning a BufferedReader to read text from the file in an efficient manner. Bytes from the file are decoded into characters using the UTF-8 charset.

This method works as if invoking it were equivalent to evaluating the expression:

Files.newBufferedReader(path, StandardCharsets.UTF_8)
 

Parameters
path Path: the path to the file

Returns
BufferedReader a new buffered reader, with default buffer size, to read text from the file

Throws
IOException if an I/O error occurs opening the file
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

newBufferedWriter

added in API level 26
public static BufferedWriter newBufferedWriter (Path path, 
                OpenOption... options)

Opens or creates a file for writing, returning a BufferedWriter to write text to the file in an efficient manner. The text is encoded into bytes for writing using the UTF-8 charset.

This method works as if invoking it were equivalent to evaluating the expression:

Files.newBufferedWriter(path, StandardCharsets.UTF_8, options)
 

Parameters
path Path: the path to the file

options OpenOption: options specifying how the file is opened

Returns
BufferedWriter a new buffered writer, with default buffer size, to write text to the file

Throws
IOException if an I/O error occurs opening or creating the file
UnsupportedOperationException if an unsupported option is specified
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

newBufferedWriter

added in API level 26
public static BufferedWriter newBufferedWriter (Path path, 
                Charset cs, 
                OpenOption... options)

Opens or creates a file for writing, returning a BufferedWriter that may be used to write text to the file in an efficient manner. The options parameter specifies how the the file is created or opened. If no options are present then this method works as if the CREATE, TRUNCATE_EXISTING, and WRITE options are present. In other words, it opens the file for writing, creating the file if it doesn't exist, or initially truncating an existing regular-file to a size of 0 if it exists.

The Writer methods to write text throw IOException if the text cannot be encoded using the specified charset.

Parameters
path Path: the path to the file

cs Charset: the charset to use for encoding

options OpenOption: options specifying how the file is opened

Returns
BufferedWriter a new buffered writer, with default buffer size, to write text to the file

Throws
IOException if an I/O error occurs opening or creating the file
UnsupportedOperationException if an unsupported option is specified
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

newByteChannel

added in API level 26
public static SeekableByteChannel newByteChannel (Path path, 
                OpenOption... options)

Opens or creates a file, returning a seekable byte channel to access the file.

This method opens or creates a file in exactly the manner specified by the newByteChannel method.

Parameters
path Path: the path to the file to open or create

options OpenOption: options specifying how the file is opened

Returns
SeekableByteChannel a new seekable byte channel

Throws
IllegalArgumentException if the set contains an invalid combination of options
UnsupportedOperationException if an unsupported open option is specified
FileAlreadyExistsException if a file of that name already exists and the CREATE_NEW option is specified (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the path if the file is opened for reading. The checkWrite method is invoked to check write access to the path if the file is opened for writing. The checkDelete method is invoked to check delete access if the file is opened with the DELETE_ON_CLOSE option.

newByteChannel

added in API level 26
public static SeekableByteChannel newByteChannel (Path path, 
                Set<? extends OpenOption> options, 
                FileAttribute...<?> attrs)

Opens or creates a file, returning a seekable byte channel to access the file.

The options parameter determines how the file is opened. The READ and WRITE options determine if the file should be opened for reading and/or writing. If neither option (or the APPEND option) is present then the file is opened for reading. By default reading or writing commence at the beginning of the file.

In the addition to READ and WRITE, the following options may be present:

Option Description
APPEND If this option is present then the file is opened for writing and each invocation of the channel's write method first advances the position to the end of the file and then writes the requested data. Whether the advancement of the position and the writing of the data are done in a single atomic operation is system-dependent and therefore unspecified. This option may not be used in conjunction with the READ or TRUNCATE_EXISTING options.
TRUNCATE_EXISTING If this option is present then the existing file is truncated to a size of 0 bytes. This option is ignored when the file is opened only for reading.
CREATE_NEW If this option is present then a new file is created, failing if the file already exists or is a symbolic link. When creating a file the check for the existence of the file and the creation of the file if it does not exist is atomic with respect to other file system operations. This option is ignored when the file is opened only for reading.
CREATE If this option is present then an existing file is opened if it exists, otherwise a new file is created. This option is ignored if the CREATE_NEW option is also present or the file is opened only for reading.
DELETE_ON_CLOSE When this option is present then the implementation makes a best effort attempt to delete the file when closed by the close method. If the close method is not invoked then a best effort attempt is made to delete the file when the Java virtual machine terminates.
SPARSE When creating a new file this option is a hint that the new file will be sparse. This option is ignored when not creating a new file.
SYNC Requires that every update to the file's content or metadata be written synchronously to the underlying storage device. (see Synchronized I/O file integrity).
DSYNC Requires that every update to the file's content be written synchronously to the underlying storage device. (see Synchronized I/O file integrity).

An implementation may also support additional implementation specific options.

The attrs parameter is optional file-attributes to set atomically when a new file is created.

In the case of the default provider, the returned seekable byte channel is a FileChannel.

Usage Examples:

     Path path = ...

     // open file for reading
     ReadableByteChannel rbc = Files.newByteChannel(path, EnumSet.of(READ)));

     // open file for writing to the end of an existing file, creating
     // the file if it doesn't already exist
     WritableByteChannel wbc = Files.newByteChannel(path, EnumSet.of(CREATE,APPEND));

     // create file with initial permissions, opening it for both reading and writing
     FileAttribute<Set<PosixFilePermission>> perms = ...
     SeekableByteChannel sbc = Files.newByteChannel(path, EnumSet.of(CREATE_NEW,READ,WRITE), perms);
 

Parameters
path Path: the path to the file to open or create

options Set: options specifying how the file is opened

attrs FileAttribute: an optional list of file attributes to set atomically when creating the file

Returns
SeekableByteChannel a new seekable byte channel

Throws
IllegalArgumentException if the set contains an invalid combination of options
UnsupportedOperationException if an unsupported open option is specified or the array contains attributes that cannot be set atomically when creating the file
FileAlreadyExistsException if a file of that name already exists and the CREATE_NEW option is specified (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the path if the file is opened for reading. The checkWrite method is invoked to check write access to the path if the file is opened for writing. The checkDelete method is invoked to check delete access if the file is opened with the DELETE_ON_CLOSE option.

newDirectoryStream

added in API level 26
public static DirectoryStream<Path> newDirectoryStream (Path dir, 
                String glob)

Opens a directory, returning a DirectoryStream to iterate over the entries in the directory. The elements returned by the directory stream's iterator are of type Path, each one representing an entry in the directory. The Path objects are obtained as if by resolving the name of the directory entry against dir. The entries returned by the iterator are filtered by matching the String representation of their file names against the given globbing pattern.

For example, suppose we want to iterate over the files ending with ".java" in a directory:

     Path dir = ...
     try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.java")) {
         :
     }
 

The globbing pattern is specified by the getPathMatcher method.

When not using the try-with-resources construct, then directory stream's close method should be invoked after iteration is completed so as to free any resources held for the open directory.

When an implementation supports operations on entries in the directory that execute in a race-free manner then the returned directory stream is a SecureDirectoryStream.

Parameters
dir Path: the path to the directory

glob String: the glob pattern

Returns
DirectoryStream<Path> a new and open DirectoryStream object

Throws
PatternSyntaxException if the pattern is invalid
NotDirectoryException if the file could not otherwise be opened because it is not a directory (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the directory.

newDirectoryStream

added in API level 26
public static DirectoryStream<Path> newDirectoryStream (Path dir, 
                Filter<? super Path> filter)

Opens a directory, returning a DirectoryStream to iterate over the entries in the directory. The elements returned by the directory stream's iterator are of type Path, each one representing an entry in the directory. The Path objects are obtained as if by resolving the name of the directory entry against dir. The entries returned by the iterator are filtered by the given filter.

When not using the try-with-resources construct, then directory stream's close method should be invoked after iteration is completed so as to free any resources held for the open directory.

Where the filter terminates due to an uncaught error or runtime exception then it is propagated to the hasNext or next method. Where an IOException is thrown, it results in the hasNext or next method throwing a DirectoryIteratorException with the IOException as the cause.

When an implementation supports operations on entries in the directory that execute in a race-free manner then the returned directory stream is a SecureDirectoryStream.

Usage Example: Suppose we want to iterate over the files in a directory that are larger than 8K.

     DirectoryStream.Filter<Path> filter = new DirectoryStream.Filter<Path>() {
         public boolean accept(Path file) throws IOException {
             return (Files.size(file) > 8192L);
         }
     };
     Path dir = ...
     try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, filter)) {
         :
     }
 

Parameters
dir Path: the path to the directory

filter Filter: the directory stream filter

Returns
DirectoryStream<Path> a new and open DirectoryStream object

Throws
NotDirectoryException if the file could not otherwise be opened because it is not a directory (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the directory.

newDirectoryStream

added in API level 26
public static DirectoryStream<Path> newDirectoryStream (Path dir)

Opens a directory, returning a DirectoryStream to iterate over all entries in the directory. The elements returned by the directory stream's iterator are of type Path, each one representing an entry in the directory. The Path objects are obtained as if by resolving the name of the directory entry against dir.

When not using the try-with-resources construct, then directory stream's close method should be invoked after iteration is completed so as to free any resources held for the open directory.

When an implementation supports operations on entries in the directory that execute in a race-free manner then the returned directory stream is a SecureDirectoryStream.

Parameters
dir Path: the path to the directory

Returns
DirectoryStream<Path> a new and open DirectoryStream object

Throws
NotDirectoryException if the file could not otherwise be opened because it is not a directory (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the directory.

newInputStream

added in API level 26
public static InputStream newInputStream (Path path, 
                OpenOption... options)

Opens a file, returning an input stream to read from the file. The stream will not be buffered, and is not required to support the mark or reset methods. The stream will be safe for access by multiple concurrent threads. Reading commences at the beginning of the file. Whether the returned stream is asynchronously closeable and/or interruptible is highly file system provider specific and therefore not specified.

The options parameter determines how the file is opened. If no options are present then it is equivalent to opening the file with the READ option. In addition to the READ option, an implementation may also support additional implementation specific options.

Parameters
path Path: the path to the file to open

options OpenOption: options specifying how the file is opened

Returns
InputStream a new input stream

Throws
IllegalArgumentException if an invalid combination of options is specified
UnsupportedOperationException if an unsupported option is specified
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

newOutputStream

added in API level 26
public static OutputStream newOutputStream (Path path, 
                OpenOption... options)

Opens or creates a file, returning an output stream that may be used to write bytes to the file. The resulting stream will not be buffered. The stream will be safe for access by multiple concurrent threads. Whether the returned stream is asynchronously closeable and/or interruptible is highly file system provider specific and therefore not specified.

This method opens or creates a file in exactly the manner specified by the newByteChannel method with the exception that the READ option may not be present in the array of options. If no options are present then this method works as if the CREATE, TRUNCATE_EXISTING, and WRITE options are present. In other words, it opens the file for writing, creating the file if it doesn't exist, or initially truncating an existing regular-file to a size of 0 if it exists.

Usage Examples:

     Path path = ...

     // truncate and overwrite an existing file, or create the file if
     // it doesn't initially exist
     OutputStream out = Files.newOutputStream(path);

     // append to an existing file, fail if the file does not exist
     out = Files.newOutputStream(path, APPEND);

     // append to an existing file, create file if it doesn't initially exist
     out = Files.newOutputStream(path, CREATE, APPEND);

     // always create new file, failing if it already exists
     out = Files.newOutputStream(path, CREATE_NEW);
 

Parameters
path Path: the path to the file to open or create

options OpenOption: options specifying how the file is opened

Returns
OutputStream a new output stream

Throws
IllegalArgumentException if options contains an invalid combination of options
UnsupportedOperationException if an unsupported option is specified
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file. The checkDelete method is invoked to check delete access if the file is opened with the DELETE_ON_CLOSE option.

notExists

added in API level 26
public static boolean notExists (Path path, 
                LinkOption... options)

Tests whether the file located by this path does not exist. This method is intended for cases where it is required to take action when it can be confirmed that a file does not exist.

The options parameter may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Note that this method is not the complement of the exists method. Where it is not possible to determine if a file exists or not then both methods return false. As with the exists method, the result of this method is immediately outdated. If this method indicates the file does exist then there is no guarantee that a subsequence attempt to create the file will succeed. Care should be taken when using this method in security sensitive applications.

Parameters
path Path: the path to the file to test

options LinkOption: options indicating how symbolic links are handled

Returns
boolean true if the file does not exist; false if the file exists or its existence cannot be determined

Throws
SecurityException In the case of the default provider, the SecurityManager.checkRead(String) is invoked to check read access to the file.

probeContentType

added in API level 26
public static String probeContentType (Path path)

Probes the content type of a file.

This method uses the installed FileTypeDetector implementations to probe the given file to determine its content type. Each file type detector's probeContentType is invoked, in turn, to probe the file type. If the file is recognized then the content type is returned. If the file is not recognized by any of the installed file type detectors then a system-default file type detector is invoked to guess the content type.

A given invocation of the Java virtual machine maintains a system-wide list of file type detectors. Installed file type detectors are loaded using the service-provider loading facility defined by the ServiceLoader class. Installed file type detectors are loaded using the system class loader. If the system class loader cannot be found then the extension class loader is used; If the extension class loader cannot be found then the bootstrap class loader is used. File type detectors are typically installed by placing them in a JAR file on the application class path or in the extension directory, the JAR file contains a provider-configuration file named java.nio.file.spi.FileTypeDetector in the resource directory META-INF/services, and the file lists one or more fully-qualified names of concrete subclass of FileTypeDetector that have a zero argument constructor. If the process of locating or instantiating the installed file type detectors fails then an unspecified error is thrown. The ordering that installed providers are located is implementation specific.

The return value of this method is the string form of the value of a Multipurpose Internet Mail Extension (MIME) content type as defined by RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. The string is guaranteed to be parsable according to the grammar in the RFC.

Parameters
path Path: the path to the file to probe

Returns
String The content type of the file, or null if the content type cannot be determined

Throws
IOException if an I/O error occurs
SecurityException If a security manager is installed and it denies an unspecified permission required by a file type detector implementation.

readAllBytes

added in API level 26
public static byte[] readAllBytes (Path path)

Reads all the bytes from a file. The method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown.

Note that this method is intended for simple cases where it is convenient to read all bytes into a byte array. It is not intended for reading in large files.

Parameters
path Path: the path to the file

Returns
byte[] a byte array containing the bytes read from the file

Throws
IOException if an I/O error occurs reading from the stream
OutOfMemoryError if an array of the required size cannot be allocated, for example the file is larger that 2GB
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

readAllLines

added in API level 26
public static List<String> readAllLines (Path path, 
                Charset cs)

Read all lines from a file. This method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown. Bytes from the file are decoded into characters using the specified charset.

This method recognizes the following as line terminators:

  • \u000D followed by \u000A, CARRIAGE RETURN followed by LINE FEED
  • \u000A, LINE FEED
  • \u000D, CARRIAGE RETURN

Additional Unicode line terminators may be recognized in future releases.

Note that this method is intended for simple cases where it is convenient to read all lines in a single operation. It is not intended for reading in large files.

Parameters
path Path: the path to the file

cs Charset: the charset to use for decoding

Returns
List<String> the lines from the file as a List; whether the List is modifiable or not is implementation dependent and therefore not specified

Throws
IOException if an I/O error occurs reading from the file or a malformed or unmappable byte sequence is read
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

readAllLines

added in API level 26
public static List<String> readAllLines (Path path)

Read all lines from a file. Bytes from the file are decoded into characters using the UTF-8 charset.

This method works as if invoking it were equivalent to evaluating the expression:

Files.readAllLines(path, StandardCharsets.UTF_8)
 

Parameters
path Path: the path to the file

Returns
List<String> the lines from the file as a List; whether the List is modifiable or not is implementation dependent and therefore not specified

Throws
IOException if an I/O error occurs reading from the file or a malformed or unmappable byte sequence is read
SecurityException In the case of the default provider, and a security manager is installed, the checkRead method is invoked to check read access to the file.

readAttributes

added in API level 26
public static Map<StringObject> readAttributes (Path path, 
                String attributes, 
                LinkOption... options)

Reads a set of file attributes as a bulk operation.

The attributes parameter identifies the attributes to be read and takes the form:

[view-name:]attribute-list
where square brackets [...] delineate an optional component and the character ':' stands for itself.

view-name is the name of a FileAttributeView that identifies a set of file attributes. If not specified then it defaults to "basic", the name of the file attribute view that identifies the basic set of file attributes common to many file systems.

The attribute-list component is a comma separated list of zero or more names of attributes to read. If the list contains the value "*" then all attributes are read. Attributes that are not supported are ignored and will not be present in the returned map. It is implementation specific if all attributes are read as an atomic operation with respect to other file system operations.

The following examples demonstrate possible values for the attributes parameter:

"*" Read all basic-file-attributes.
"size,lastModifiedTime,lastAccessTime" Reads the file size, last modified time, and last access time attributes.
"posix:*" Read all POSIX-file-attributes.
"posix:permissions,owner,size" Reads the POSX file permissions, owner, and file size.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Parameters
path Path: the path to the file

attributes String: the attributes to read

options LinkOption: options indicating how symbolic links are handled

Returns
Map<StringObject> a map of the attributes returned; The map's keys are the attribute names, its values are the attribute values

Throws
UnsupportedOperationException if the attribute view is not available
IllegalArgumentException if no attributes are specified or an unrecognized attributes is specified
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file. If this method is invoked to read security sensitive attributes then the security manager may be invoke to check for additional permissions.

readAttributes

added in API level 26
public static A readAttributes (Path path, 
                Class<A> type, 
                LinkOption... options)

Reads a file's attributes as a bulk operation.

The type parameter is the type of the attributes required and this method returns an instance of that type if supported. All implementations support a basic set of file attributes and so invoking this method with a type parameter of BasicFileAttributes.class will not throw UnsupportedOperationException.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is read. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

It is implementation specific if all file attributes are read as an atomic operation with respect to other file system operations.

Usage Example: Suppose we want to read a file's attributes in bulk:

    Path path = ...
    BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class);
 
Alternatively, suppose we want to read file's POSIX attributes without following symbolic links:
    PosixFileAttributes attrs = Files.readAttributes(path, PosixFileAttributes.class, NOFOLLOW_LINKS);
 

Parameters
path Path: the path to the file

type Class: the Class of the file attributes required to read

options LinkOption: options indicating how symbolic links are handled

Returns
A the file attributes

Throws
UnsupportedOperationException if an attributes of the given type are not supported
IOException if an I/O error occurs
SecurityException In the case of the default provider, a security manager is installed, its checkRead method is invoked to check read access to the file. If this method is invoked to read security sensitive attributes then the security manager may be invoke to check for additional permissions.

readSymbolicLink

added in API level 26
public static Path readSymbolicLink (Path link)

Reads the target of a symbolic link (optional operation).

If the file system supports symbolic links then this method is used to read the target of the link, failing if the file is not a symbolic link. The target of the link need not exist. The returned Path object will be associated with the same file system as link.

Parameters
link Path: the path to the symbolic link

Returns
Path a Path object representing the target of the link

Throws
UnsupportedOperationException if the implementation does not support symbolic links
NotLinkException if the target could otherwise not be read because the file is not a symbolic link (optional specific exception)
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it checks that FilePermission has been granted with the "readlink" action to read the link.

setAttribute

added in API level 26
public static Path setAttribute (Path path, 
                String attribute, 
                Object value, 
                LinkOption... options)

Sets the value of a file attribute.

The attribute parameter identifies the attribute to be set and takes the form:

[view-name:]attribute-name
where square brackets [...] delineate an optional component and the character ':' stands for itself.

view-name is the name of a FileAttributeView that identifies a set of file attributes. If not specified then it defaults to "basic", the name of the file attribute view that identifies the basic set of file attributes common to many file systems. attribute-name is the name of the attribute within the set.

The options array may be used to indicate how symbolic links are handled for the case that the file is a symbolic link. By default, symbolic links are followed and the file attribute of the final target of the link is set. If the option NOFOLLOW_LINKS is present then symbolic links are not followed.

Usage Example: Suppose we want to set the DOS "hidden" attribute:

    Path path = ...
    Files.setAttribute(path, "dos:hidden", true);
 

Parameters
path Path: the path to the file

attribute String: the attribute to set

value Object: the attribute value

options LinkOption: options indicating how symbolic links are handled

Returns
Path the path parameter

Throws
UnsupportedOperationException if the attribute view is not available
IllegalArgumentException if the attribute name is not specified, or is not recognized, or the attribute value is of the correct type but has an inappropriate value
ClassCastException if the attribute value is not of the expected type or is a collection containing elements that are not of the expected type
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, its checkWrite method denies write access to the file. If this method is invoked to set security sensitive attributes then the security manager may be invoked to check for additional permissions.

setLastModifiedTime

added in API level 26
public static Path setLastModifiedTime (Path path, 
                FileTime time)

Updates a file's last modified time attribute. The file time is converted to the epoch and precision supported by the file system. Converting from finer to coarser granularities result in precision loss. The behavior of this method when attempting to set the last modified time when it is not supported by the file system or is outside the range supported by the underlying file store is not defined. It may or not fail by throwing an IOException.

Usage Example: Suppose we want to set the last modified time to the current time:

    Path path = ...
    FileTime now = FileTime.fromMillis(System.currentTimeMillis());
    Files.setLastModifiedTime(path, now);
 

Parameters
path Path: the path to the file

time FileTime: the new last modified time

Returns
Path the path

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, the security manager's checkWrite method is invoked to check write access to file

setOwner

added in API level 26
public static Path setOwner (Path path, 
                UserPrincipal owner)

Updates the file owner.

The path parameter is associated with a file system that supports FileOwnerAttributeView. This file attribute view provides access to a file attribute that is the owner of the file.

Usage Example: Suppose we want to make "joe" the owner of a file:

     Path path = ...
     UserPrincipalLookupService lookupService =
         provider(path).getUserPrincipalLookupService();
     UserPrincipal joe = lookupService.lookupPrincipalByName("joe");
     Files.setOwner(path, joe);
 

Parameters
path Path: The path to the file

owner UserPrincipal: The new file owner

Returns
Path The path

Throws
UnsupportedOperationException if the associated file system does not support the FileOwnerAttributeView
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it denies RuntimePermission("accessUserInformation") or its checkWrite method denies write access to the file.

setPosixFilePermissions

added in API level 26
public static Path setPosixFilePermissions (Path path, 
                Set<PosixFilePermission> perms)

Sets a file's POSIX permissions.

The path parameter is associated with a FileSystem that supports the PosixFileAttributeView. This attribute view provides access to file attributes commonly associated with files on file systems used by operating systems that implement the Portable Operating System Interface (POSIX) family of standards.

Parameters
path Path: The path to the file

perms Set: The new set of permissions

Returns
Path The path

Throws
UnsupportedOperationException if the associated file system does not support the PosixFileAttributeView
ClassCastException if the sets contains elements that are not of type PosixFilePermission
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, it denies RuntimePermission("accessUserInformation") or its checkWrite method denies write access to the file.

size

added in API level 26
public static long size (Path path)

Returns the size of a file (in bytes). The size may differ from the actual size on the file system due to compression, support for sparse files, or other reasons. The size of files that are not regular files is implementation specific and therefore unspecified.

Parameters
path Path: the path to the file

Returns
long the file size, in bytes

Throws
IOException if an I/O error occurs
SecurityException In the case of the default provider, and a security manager is installed, its checkRead method denies read access to the file.

walk

added in API level 26
public static Stream<Path> walk (Path start, 
                FileVisitOption... options)

Return a Stream that is lazily populated with Path by walking the file tree rooted at a given starting file. The file tree is traversed depth-first, the elements in the stream are Path objects that are obtained as if by resolving the relative path against start.

This method works as if invoking it were equivalent to evaluating the expression:

 walk(start, Integer.MAX_VALUE, options)
 
In other words, it visits all levels of the file tree.

The returned stream encapsulates one or more DirectoryStreams. If timely disposal of file system resources is required, the try-with-resources construct should be used to ensure that the stream's close method is invoked after the stream operations are completed. Operating on a closed stream will result in an IllegalStateException.

Parameters
start Path: the starting file

options FileVisitOption: options to configure the traversal

Returns
Stream<Path> the Stream of Path

Throws
SecurityException If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.
IOException if an I/O error is thrown when accessing the starting file.

walk

added in API level 26
public static Stream<Path> walk (Path start, 
                int maxDepth, 
                FileVisitOption... options)

Return a Stream that is lazily populated with Path by walking the file tree rooted at a given starting file. The file tree is traversed depth-first, the elements in the stream are Path objects that are obtained as if by resolving the relative path against start.

The stream walks the file tree as elements are consumed. The Stream returned is guaranteed to have at least one element, the starting file itself. For each file visited, the stream attempts to read its BasicFileAttributes. If the file is a directory and can be opened successfully, entries in the directory, and their descendants will follow the directory in the stream as they are encountered. When all entries have been visited, then the directory is closed. The file tree walk then continues at the next sibling of the directory.

The stream is weakly consistent. It does not freeze the file tree while iterating, so it may (or may not) reflect updates to the file tree that occur after returned from this method.

By default, symbolic links are not automatically followed by this method. If the options parameter contains the FOLLOW_LINKS option then symbolic links are followed. When following links, and the attributes of the target cannot be read, then this method attempts to get the BasicFileAttributes of the link.

If the options parameter contains the FOLLOW_LINKS option then the stream keeps track of directories visited so that cycles can be detected. A cycle arises when there is an entry in a directory that is an ancestor of the directory. Cycle detection is done by recording the file-key of directories, or if file keys are not available, by invoking the isSameFile method to test if a directory is the same file as an ancestor. When a cycle is detected it is treated as an I/O error with an instance of FileSystemLoopException.

The maxDepth parameter is the maximum number of levels of directories to visit. A value of 0 means that only the starting file is visited, unless denied by the security manager. A value of MAX_VALUE may be used to indicate that all levels should be visited.

When a security manager is installed and it denies access to a file (or directory), then it is ignored and not included in the stream.

The returned stream encapsulates one or more DirectoryStreams. If timely disposal of file system resources is required, the try-with-resources construct should be used to ensure that the stream's close method is invoked after the stream operations are completed. Operating on a closed stream will result in an IllegalStateException.

If an IOException is thrown when accessing the directory after this method has returned, it is wrapped in an UncheckedIOException which will be thrown from the method that caused the access to take place.

Parameters
start Path: the starting file

maxDepth int: the maximum number of directory levels to visit

options FileVisitOption: options to configure the traversal

Returns
Stream<Path> the Stream of Path

Throws
IllegalArgumentException if the maxDepth parameter is negative
SecurityException If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.
IOException if an I/O error is thrown when accessing the starting file.

walkFileTree

added in API level 26
public static Path walkFileTree (Path start, 
                FileVisitor<? super Path> visitor)

Walks a file tree.

This method works as if invoking it were equivalent to evaluating the expression:

 walkFileTree(start, EnumSet.noneOf(FileVisitOption.class), Integer.MAX_VALUE, visitor)
 
In other words, it does not follow symbolic links, and visits all levels of the file tree.

Parameters
start Path: the starting file

visitor FileVisitor: the file visitor to invoke for each file

Returns
Path the starting file

Throws
SecurityException If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.
IOException if an I/O error is thrown by a visitor method

walkFileTree

added in API level 26
public static Path walkFileTree (Path start, 
                Set<FileVisitOption> options, 
                int maxDepth, 
                FileVisitor<? super Path> visitor)

Walks a file tree.

This method walks a file tree rooted at a given starting file. The file tree traversal is depth-first with the given FileVisitor invoked for each file encountered. File tree traversal completes when all accessible files in the tree have been visited, or a visit method returns a result of TERMINATE. Where a visit method terminates due an IOException, an uncaught error, or runtime exception, then the traversal is terminated and the error or exception is propagated to the caller of this method.

For each file encountered this method attempts to read its BasicFileAttributes. If the file is not a directory then the visitFile method is invoked with the file attributes. If the file attributes cannot be read, due to an I/O exception, then the visitFileFailed method is invoked with the I/O exception.

Where the file is a directory, and the directory could not be opened, then the visitFileFailed method is invoked with the I/O exception, after which, the file tree walk continues, by default, at the next sibling of the directory.

Where the directory is opened successfully, then the entries in the directory, and their descendants are visited. When all entries have been visited, or an I/O error occurs during iteration of the directory, then the directory is closed and the visitor's postVisitDirectory method is invoked. The file tree walk then continues, by default, at the next sibling of the directory.

By default, symbolic links are not automatically followed by this method. If the options parameter contains the FOLLOW_LINKS option then symbolic links are followed. When following links, and the attributes of the target cannot be read, then this method attempts to get the BasicFileAttributes of the link. If they can be read then the visitFile method is invoked with the attributes of the link (otherwise the visitFileFailed method is invoked as specified above).

If the options parameter contains the FOLLOW_LINKS option then this method keeps track of directories visited so that cycles can be detected. A cycle arises when there is an entry in a directory that is an ancestor of the directory. Cycle detection is done by recording the file-key of directories, or if file keys are not available, by invoking the isSameFile method to test if a directory is the same file as an ancestor. When a cycle is detected it is treated as an I/O error, and the visitFileFailed method is invoked with an instance of FileSystemLoopException.

The maxDepth parameter is the maximum number of levels of directories to visit. A value of 0 means that only the starting file is visited, unless denied by the security manager. A value of MAX_VALUE may be used to indicate that all levels should be visited. The visitFile method is invoked for all files, including directories, encountered at maxDepth, unless the basic file attributes cannot be read, in which case the visitFileFailed method is invoked.

If a visitor returns a result of null then NullPointerException is thrown.

When a security manager is installed and it denies access to a file (or directory), then it is ignored and the visitor is not invoked for that file (or directory).

Parameters
start Path: the starting file

options Set: options to configure the traversal

maxDepth int: the maximum number of directory levels to visit

visitor FileVisitor: the file visitor to invoke for each file

Returns
Path the starting file

Throws
IllegalArgumentException if the maxDepth parameter is negative
SecurityException If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.
IOException if an I/O error is thrown by a visitor method

write

added in API level 26
public static Path write (Path path, 
                Iterable<? extends CharSequence> lines, 
                OpenOption... options)

Write lines of text to a file. Characters are encoded into bytes using the UTF-8 charset.

This method works as if invoking it were equivalent to evaluating the expression:

Files.write(path, lines, StandardCharsets.UTF_8, options);
 

Parameters
path Path: the path to the file

lines Iterable: an object to iterate over the char sequences

options OpenOption: options specifying how the file is opened

Returns
Path the path

Throws
IOException if an I/O error occurs writing to or creating the file, or the text cannot be encoded as UTF-8
UnsupportedOperationException if an unsupported option is specified
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

write

added in API level 26
public static Path write (Path path, 
                Iterable<? extends CharSequence> lines, 
                Charset cs, 
                OpenOption... options)

Write lines of text to a file. Each line is a char sequence and is written to the file in sequence with each line terminated by the platform's line separator, as defined by the system property line.separator. Characters are encoded into bytes using the specified charset.

The options parameter specifies how the the file is created or opened. If no options are present then this method works as if the CREATE, TRUNCATE_EXISTING, and WRITE options are present. In other words, it opens the file for writing, creating the file if it doesn't exist, or initially truncating an existing regular-file to a size of 0. The method ensures that the file is closed when all lines have been written (or an I/O error or other runtime exception is thrown). If an I/O error occurs then it may do so after the file has created or truncated, or after some bytes have been written to the file.

Parameters
path Path: the path to the file

lines Iterable: an object to iterate over the char sequences

cs Charset: the charset to use for encoding

options OpenOption: options specifying how the file is opened

Returns
Path the path

Throws
IOException if an I/O error occurs writing to or creating the file, or the text cannot be encoded using the specified charset
UnsupportedOperationException if an unsupported option is specified
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.

write

added in API level 26
public static Path write (Path path, 
                byte[] bytes, 
                OpenOption... options)

Writes bytes to a file. The options parameter specifies how the the file is created or opened. If no options are present then this method works as if the CREATE, TRUNCATE_EXISTING, and WRITE options are present. In other words, it opens the file for writing, creating the file if it doesn't exist, or initially truncating an existing regular-file to a size of 0. All bytes in the byte array are written to the file. The method ensures that the file is closed when all bytes have been written (or an I/O error or other runtime exception is thrown). If an I/O error occurs then it may do so after the file has created or truncated, or after some bytes have been written to the file.

Usage example: By default the method creates a new file or overwrites an existing file. Suppose you instead want to append bytes to an existing file:

     Path path = ...
     byte[] bytes = ...
     Files.write(path, bytes, StandardOpenOption.APPEND);
 

Parameters
path Path: the path to the file

bytes byte: the byte array with the bytes to write

options OpenOption: options specifying how the file is opened

Returns
Path the path

Throws
IOException if an I/O error occurs writing to or creating the file
UnsupportedOperationException if an unsupported option is specified
SecurityException In the case of the default provider, and a security manager is installed, the checkWrite method is invoked to check write access to the file.