Package java.io

Class FilterInputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

ASN1InputStream, BufferedInputStream, CheckedInputStream, CipherInputStream, DataInputStream, DeflaterInputStream, DigestInputStream, DigestInputStream, InflaterInputStream, LineNumberInputStream, MacInputStream, OpenSSLBIOInputStream, PushbackInputStream

public class FilterInputStream
extends InputStream

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:

FilterOutputStream

Field Summary

Fields

Modifier and Type	Field	Description
protected InputStream	in	The source input stream that is filtered.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	FilterInputStream(InputStream in)	Constructs a new FilterInputStream with the specified input stream as source.

Method Summary

Modifier and Type	Method	Description
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 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 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 byteCount bytes in this stream.

Methods inherited from class java.io.InputStream

read

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

in

protected volatile InputStream in

The source input stream that is filtered.

Constructor Detail

FilterInputStream

protected FilterInputStream(InputStream in)

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.

Method Detail

available

public int available()
              throws IOException

Description copied from class: InputStream

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, 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.

Overrides:

available in class InputStream

Returns:

the estimated number of bytes available

Throws:

IOException - if this stream is closed or an error occurs

close

public void close()
           throws IOException

Closes this stream. This implementation closes the filtered stream.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Overrides:

close in class InputStream

Throws:

IOException - if an error occurs while closing this stream.

mark

public void mark(int readlimit)

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.

Overrides:

mark in class InputStream

Parameters:

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

See Also:

markSupported(), reset()

markSupported

public boolean markSupported()

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

Overrides:

markSupported in class InputStream

Returns:

true if mark() and reset() are supported, false otherwise.

See Also:

mark(int), reset(), skip(long)

read

public int read()
         throws IOException

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.

Specified by:

read in class InputStream

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.

read

public int read(byte[] buffer,
                int byteOffset,
                int byteCount)
         throws IOException

Description copied from class: InputStream

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.

Overrides:

read in class InputStream

Throws:

IOException - if the stream is closed or another IOException occurs.

reset

public void reset()
           throws IOException

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

Overrides:

reset in class InputStream

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:

mark(int), markSupported()

skip

public long skip(long byteCount)
          throws IOException

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.

Overrides:

skip in class InputStream

Returns:

the number of bytes actually skipped.

Throws:

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

See Also:

mark(int), reset()