public class

FilterInputStream

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

Class Overview

Wraps an existing InputStream and performs some transformation on the input data while it is being read. Transformations can be anything from a simple byte-wise filtering input data to an on-the-fly compression or decompression of the underlying stream. Input streams that wrap another input stream and provide some additional functionality on top of it usually inherit from this class.

See Also

Summary

Fields
protected InputStream in The source input stream that is filtered.
Protected Constructors
FilterInputStream(InputStream in)
Constructs a new FilterInputStream with the specified input stream as source.
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.
synchronized void mark(int readlimit)
Sets a mark position in this stream.
boolean markSupported()
Indicates whether this stream supports mark() and reset().
int read()
Reads a single byte from the filtered stream and returns it as an integer in the range from 0 to 255.
int read(byte[] buffer, int offset, int count)
Reads at most count bytes from this stream and stores them in the byte array buffer starting at offset.
synchronized void reset()
Resets this stream to the last marked location.
long skip(long byteCount)
Skips byteCount bytes in this stream.
[Expand]
Inherited Methods
From class java.io.InputStream
From class java.lang.Object
From interface java.io.Closeable

Fields

protected InputStream in

Since: API Level 1

The source input stream that is filtered.

Protected Constructors

protected FilterInputStream (InputStream in)

Since: API Level 1

Constructs a new FilterInputStream with the specified input stream as source.

Warning: passing a null source creates an invalid FilterInputStream, that fails on every method that is not overridden. Subclasses should check for null in their constructors.

Parameters
in the input stream to filter reads on.

Public Methods

public int available ()

Since: API Level 1

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
  • the estimated number of bytes available
Throws
IOException

public void close ()

Since: API Level 1

Closes this stream. This implementation closes the filtered stream.

Throws
IOException if an error occurs while closing this stream.

public synchronized void mark (int readlimit)

Since: API Level 1

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

This implementation sets a mark in the filtered stream.

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

public boolean markSupported ()

Since: API Level 1

Indicates whether this stream supports mark() and reset(). This implementation returns whether or not the filtered stream supports marking.

Returns
  • true if mark() and reset() are supported, false otherwise.
See Also

public int read ()

Since: API Level 1

Reads a single byte from the filtered stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of this stream has been reached.

Returns
  • the byte read or -1 if the end of the filtered stream has been reached.
Throws
IOException if the stream is closed or another IOException occurs.

public int read (byte[] buffer, int offset, int count)

Since: API Level 1

Reads at most count bytes from this stream and stores them in the byte array buffer starting at offset. Returns the number of bytes actually read or -1 if no bytes have been read and the end of this stream has been reached. This implementation reads bytes from the filtered stream.

Parameters
buffer the byte array in which to store the bytes read.
offset the initial position in buffer to store the bytes read from this stream.
count the maximum number of bytes to store in buffer.
Returns
  • the number of bytes actually read or -1 if the end of the filtered stream has been reached while reading.
Throws
IOException if this stream is closed or another I/O error occurs.

public synchronized void reset ()

Since: API Level 1

Resets this stream to the last marked location. This implementation resets the target stream.

Throws
IOException if this stream is already closed, no mark has been set or the mark is no longer valid because more than readlimit bytes have been read since setting the mark.
See Also

public long skip (long byteCount)

Since: API Level 1

Skips byteCount bytes in this stream. Subsequent calls to read will not return these bytes unless reset is used. This implementation skips byteCount bytes in the filtered stream.

Parameters
byteCount the number of bytes to skip.
Returns
  • the number of bytes actually skipped.
Throws
IOException if this stream is closed or another IOException occurs.
See Also