Skip to content

Most visited

Recently visited

navigation
Added in API level 1

InputStream

public abstract class InputStream
extends Object implements Closeable

java.lang.Object
   ↳ java.io.InputStream
Known Direct Subclasses
Known Indirect Subclasses


A readable source of bytes.

Most clients will use input streams that read data from the file system (FileInputStream), the network (getInputStream()/getInputStream()), or from an in-memory byte array (ByteArrayInputStream).

Use InputStreamReader to adapt a byte stream like this one into a character stream.

Most clients should wrap their input stream with BufferedInputStream. Callers that do only bulk reads may omit buffering.

Some implementations support marking a position in the input stream and resetting back to this position later. Implementations that don't return false from markSupported() and throw an IOException when reset() is called.

Subclassing InputStream

Subclasses that decorate another input stream should consider subclassing FilterInputStream, which delegates all calls to the source input stream.

All input stream subclasses should override both read() and read(byte[],int,int). The three argument overload is necessary for bulk access to the data. This is much more efficient than byte-by-byte access.

See also:

Summary

Public constructors

InputStream()

This constructor does nothing.

Public methods

int available()

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

void close()

Closes this stream.

void mark(int readlimit)

Sets a mark position in this InputStream.

boolean markSupported()

Indicates whether this stream supports the mark() and reset() methods.

int read(byte[] buffer)

Equivalent to read(buffer, 0, buffer.length).

abstract int read()

Reads a single byte from this stream and returns it as an integer in the range from 0 to 255.

int read(byte[] buffer, int byteOffset, int byteCount)

Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset.

void reset()

Resets this stream to the last marked location.

long skip(long byteCount)

Skips at most byteCount bytes in this stream.

Inherited methods

From class java.lang.Object
From interface java.io.Closeable
From interface java.lang.AutoCloseable

Public constructors

InputStream

Added in API level 1
InputStream ()

This constructor does nothing. It is provided for signature compatibility.

Public methods

available

Added in API level 1
int available ()

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

Note that this method provides such a weak guarantee that it is not very useful in practice.

Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

Returns
int the estimated number of bytes available
Throws
IOException if this stream is closed or an error occurs

close

Added in API level 1
void close ()

Closes this stream. Concrete implementations of this class should free any resources during close. This implementation does nothing.

Throws
IOException if an error occurs while closing this stream.

mark

Added in API level 1
void mark (int readlimit)

Sets a mark position in this InputStream. The parameter readlimit indicates how many bytes can be read before the mark is invalidated. Sending reset() will reposition the stream back to the marked position provided readLimit has not been surpassed.

This default implementation does nothing and concrete subclasses must provide their own implementation.

Parameters
readlimit int: the number of bytes that can be read from this stream before the mark is invalidated.

See also:

markSupported

Added in API level 1
boolean markSupported ()

Indicates whether this stream supports the mark() and reset() methods. The default implementation returns false.

Returns
boolean always false.

See also:

read

Added in API level 1
int read (byte[] buffer)

Equivalent to read(buffer, 0, buffer.length).

Parameters
buffer byte
Returns
int
Throws
IOException

read

Added in API level 1
int read ()

Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the stream has been reached. Blocks until one byte has been read, the end of the source stream is detected or an exception is thrown.

Returns
int
Throws
IOException if the stream is closed or another IOException occurs.

read

Added in API level 1
int read (byte[] buffer, 
                int byteOffset, 
                int byteCount)

Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset. Returns the number of bytes actually read or -1 if the end of the stream has been reached.

Parameters
buffer byte
byteOffset int
byteCount int
Returns
int
Throws
IndexOutOfBoundsException if byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length.
IOException if the stream is closed or another IOException occurs.

reset

Added in API level 1
void reset ()

Resets this stream to the last marked location. Throws an IOException if the number of bytes read since the mark has been set is greater than the limit provided to mark, or if no mark has been set.

This implementation always throws an IOException and concrete subclasses should provide the proper implementation.

Throws
IOException if this stream is closed or another IOException occurs.

skip

Added in API level 1
long skip (long byteCount)

Skips at most byteCount bytes in this stream. The number of actual bytes skipped may be anywhere between 0 and byteCount. If byteCount is negative, this method does nothing and returns 0, but some subclasses may throw.

Note the "at most" in the description of this method: this method may choose to skip fewer bytes than requested. Callers should always check the return value.

This default implementation reads bytes into a temporary buffer. Concrete subclasses should provide their own implementation.

Parameters
byteCount long
Returns
long the number of bytes actually skipped.
Throws
IOException if this stream is closed or another IOException occurs.
This site uses cookies to store your preferences for site-specific language and display options.

Hooray!

This class requires API level or higher

This doc is hidden because your selected API level for the documentation is . You can change the documentation API level with the selector above the left navigation.

For more information about specifying the API level your app requires, read Supporting Different Platform Versions.