# FileVisitor Added in[API level 26](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) # FileVisitor ``` interface FileVisitor ``` |--------------------------------------------------------------------------------------------------------| | [java.nio.file.FileVisitor](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#) | |-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Known Direct Subclasses [SimpleFileVisitor](https://developer.android.com/reference/kotlin/java/nio/file/SimpleFileVisitor) |-----------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------| | [SimpleFileVisitor](https://developer.android.com/reference/kotlin/java/nio/file/SimpleFileVisitor) | A simple visitor of files with default behavior to visit all files and to re-throw I/O errors. | | A visitor of files. An implementation of this interface is provided to the java.nio.file.Files#walkFileTree methods to visit each file in a file tree. **Usage Examples:**Suppose we want to delete a file tree. In that case, each directory should be deleted after the entries in the directory are deleted. ```kotlin Path start = ... Files.walkFileTree(start, new SimpleFileVisitor() { @Override public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException { Files.delete(file); return FileVisitResult.CONTINUE; } @Override public FileVisitResult postVisitDirectory(Path dir, IOException e) throws IOException { if (e == null) { Files.delete(dir); return FileVisitResult.CONTINUE; } else { // directory iteration failed throw e; } } }); ``` Furthermore, suppose we want to copy a file tree to a target location. In that case, symbolic links should be followed and the target directory should be created before the entries in the directory are copied. ```kotlin final Path source = ... final Path target = ... Files.walkFileTree(source, EnumSet.of(FileVisitOption.FOLLOW_LINKS), Integer.MAX_VALUE, new SimpleFileVisitor() { @Override public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException { Path targetdir = target.resolve(source.relativize(dir)); try { Files.copy(dir, targetdir); } catch (FileAlreadyExistsException e) { if (!Files.isDirectory(targetdir)) throw e; } return CONTINUE; } @Override public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException { Files.copy(file, target.resolve(source.relativize(file))); return CONTINUE; } }); ``` ## Summary | Public methods || |----------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | abstract[FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | [postVisitDirectory](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#postVisitDirectory(java.nio.file.FileVisitor.T,%20java.io.IOException))`(`dir:` `T`, `exc:` `[IOException](https://developer.android.com/reference/kotlin/java/io/IOException.html#)!`)` Invoked for a directory after entries in the directory, and all of their descendants, have been visited. | | abstract[FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | [preVisitDirectory](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#preVisitDirectory(java.nio.file.FileVisitor.T,%20java.nio.file.attribute.BasicFileAttributes))`(`dir:` `T`, `attrs:` `[BasicFileAttributes](https://developer.android.com/reference/kotlin/java/nio/file/attribute/BasicFileAttributes)!`)` Invoked for a directory before entries in the directory are visited. | | abstract[FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | [visitFile](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#visitFile(java.nio.file.FileVisitor.T,%20java.nio.file.attribute.BasicFileAttributes))`(`file:` `T`, `attrs:` `[BasicFileAttributes](https://developer.android.com/reference/kotlin/java/nio/file/attribute/BasicFileAttributes)!`)` Invoked for a file in a directory. | | abstract[FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | [visitFileFailed](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#visitFileFailed(java.nio.file.FileVisitor.T,%20java.io.IOException))`(`file:` `T`, `exc:` `[IOException](https://developer.android.com/reference/kotlin/java/io/IOException.html#)!`)` Invoked for a file that could not be visited. | ## Public methods ### postVisitDirectory Added in[API level 26](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun postVisitDirectory(     dir: T,     exc: IOException! ): FileVisitResult! ``` Invoked for a directory after entries in the directory, and all of their descendants, have been visited. This method is also invoked when iteration of the directory completes prematurely (by a[visitFile](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitor#visitFile(java.nio.file.FileVisitor.T,%20java.nio.file.attribute.BasicFileAttributes))method returning[SKIP_SIBLINGS](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult), or an I/O error when iterating over the directory). | Parameters || |-------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `dir` | T:a reference to the directory | | `exc` | [IOException](https://developer.android.com/reference/kotlin/java/io/IOException.html#)!:`null`if the iteration of the directory completes without an error; otherwise the I/O exception that caused the iteration of the directory to complete prematurely | | Return || |--------------------------------------------------------------------------------------------------|------------------| | [FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | the visit result | | Exceptions || |-----------------------|------------------------| | `java.io.IOException` | if an I/O error occurs | ### preVisitDirectory Added in[API level 26](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun preVisitDirectory(     dir: T,     attrs: BasicFileAttributes! ): FileVisitResult! ``` Invoked for a directory before entries in the directory are visited. If this method returns[CONTINUE](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult), then entries in the directory are visited. If this method returns[SKIP_SUBTREE](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)or[SKIP_SIBLINGS](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)then entries in the directory (and any descendants) will not be visited. | Parameters || |---------|-----------------------------------------------------------------------------------------------------------------------------------------------------| | `dir` | T:a reference to the directory | | `attrs` | [BasicFileAttributes](https://developer.android.com/reference/kotlin/java/nio/file/attribute/BasicFileAttributes)!:the directory's basic attributes | | Return || |--------------------------------------------------------------------------------------------------|------------------| | [FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | the visit result | | Exceptions || |-----------------------|------------------------| | `java.io.IOException` | if an I/O error occurs | ### visitFile Added in[API level 26](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun visitFile(     file: T,     attrs: BasicFileAttributes! ): FileVisitResult! ``` Invoked for a file in a directory. | Parameters || |---------|------------------------------------------------------------------------------------------------------------------------------------------------| | `file` | T:a reference to the file | | `attrs` | [BasicFileAttributes](https://developer.android.com/reference/kotlin/java/nio/file/attribute/BasicFileAttributes)!:the file's basic attributes | | Return || |--------------------------------------------------------------------------------------------------|------------------| | [FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | the visit result | | Exceptions || |-----------------------|------------------------| | `java.io.IOException` | if an I/O error occurs | ### visitFileFailed Added in[API level 26](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` abstract fun visitFileFailed(     file: T,     exc: IOException! ): FileVisitResult! ``` Invoked for a file that could not be visited. This method is invoked if the file's attributes could not be read, the file is a directory that could not be opened, and other reasons. | Parameters || |--------|-------------------------------------------------------------------------------------------------------------------------------------------------------| | `file` | T:a reference to the file | | `exc` | [IOException](https://developer.android.com/reference/kotlin/java/io/IOException.html#)!:the I/O exception that prevented the file from being visited | | Return || |--------------------------------------------------------------------------------------------------|------------------| | [FileVisitResult](https://developer.android.com/reference/kotlin/java/nio/file/FileVisitResult)! | the visit result | | Exceptions || |-----------------------|------------------------| | `java.io.IOException` | if an I/O error occurs |