FilterInputStream

public class FilterInputStream extends InputStream

Known Direct Subclasses BufferedInputStream, CheckedInputStream, CipherInputStream, DataInputStream, DeflaterInputStream, DigestInputStream, InflaterInputStream, LineNumberInputStream, PushbackInputStream BufferedInputStream A BufferedInputStream adds functionality to another input stream-namely, the ability to buffer the input and to support the mark and reset methods.  CheckedInputStream An input stream that also maintains a checksum of the data being read.  CipherInputStream A CipherInputStream is composed of an InputStream and a Cipher so that read() methods return data that are read in from the underlying InputStream but have been additionally processed by the Cipher.  DataInputStream A data input stream lets an application read primitive Java data types from an underlying input stream in a machine-independent way.  DeflaterInputStream Implements an input stream filter for compressing data in the "deflate" compression format.  DigestInputStream A transparent stream that updates the associated message digest using the bits going through the stream.  InflaterInputStream This class implements a stream filter for uncompressing data in the "deflate" compression format.  LineNumberInputStream This class is deprecated. This class incorrectly assumes that bytes adequately represent characters. As of JDK 1.1, the preferred way to operate on character streams is via the new character-stream classes, which include a class for counting line numbers.   PushbackInputStream A PushbackInputStream adds functionality to another input stream, namely the ability to "push back" or "unread" one byte.

Known Indirect Subclasses GZIPInputStream, JarInputStream, ZipInputStream GZIPInputStream This class implements a stream filter for reading compressed data in the GZIP file format.  JarInputStream The JarInputStream class is used to read the contents of a JAR file from any input stream.  ZipInputStream This class implements an input stream filter for reading files in the ZIP file format.

A FilterInputStream contains some other input stream, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality. The class FilterInputStream itself simply overrides all methods of InputStream with versions that pass all requests to the contained input stream. Subclasses of FilterInputStream may further override some of these methods and may also provide additional methods and fields.

Field Summary

protected InputStream

in

The input stream to be filtered.

Protected Constructor Summary

FilterInputStream(InputStream in) Creates a FilterInputStream by assigning the argument in to the field this.in so as to remember it for later use.

Public Method Summary

int	available() Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream.
void	close() Closes this input stream and releases any system resources associated with the stream.
synchronized void	mark(int readlimit) Marks the current position in this input stream.
boolean	markSupported() Tests if this input stream supports the mark and reset methods.
int	read() Reads the next byte of data from this input stream.
int	read(byte[] b, int off, int len) Reads up to len bytes of data from this input stream into an array of bytes.
int	read(byte[] b) Reads up to byte.length bytes of data from this input stream into an array of bytes.
synchronized void	reset() Repositions this stream to the position at the time the mark method was last called on this input stream.
long	skip(long n) Skips over and discards n bytes of data from the input stream.

Inherited Method Summary

From class java.io.InputStream

int	available() Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
void	close() Closes this input stream and releases any system resources associated with the stream.
synchronized void	mark(int readlimit) Marks the current position in this input stream.
boolean	markSupported() Tests if this input stream supports the mark and reset methods.
abstract int	read() Reads the next byte of data from the input stream.
int	read(byte[] b, int off, int len) Reads up to len bytes of data from the input stream into an array of bytes.
int	read(byte[] b) Reads some number of bytes from the input stream and stores them into the buffer array b.
synchronized void	reset() Repositions this stream to the position at the time the mark method was last called on this input stream.
long	skip(long n) Skips over and discards n bytes of data from this input stream.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Fields

protected InputStream in

The input stream to be filtered.

Protected Constructors

protected FilterInputStream (InputStream in)

Creates a FilterInputStream by assigning the argument in to the field this.in so as to remember it for later use.

Parameters

in	the underlying input stream, or null if this instance is to be created without an underlying stream.

Public Methods

public int available ()

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next caller of a method for this input stream. The next caller might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

This method returns the result of in.available().

Returns

• an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking.

Throws

IOException	if an I/O error occurs.

public void close ()

Closes this input stream and releases any system resources associated with the stream. This method simply performs in.close().

Throws

IOException	if an I/O error occurs.

See Also

• in

public synchronized void mark (int readlimit)

Marks the current position in this input stream. A subsequent call to the reset method repositions this stream at the last marked position so that subsequent reads re-read the same bytes.

The readlimit argument tells this input stream to allow that many bytes to be read before the mark position gets invalidated.

This method simply performs in.mark(readlimit).

Parameters

readlimit	the maximum limit of bytes that can be read before the mark position becomes invalid.

See Also

• in
• reset()

public boolean markSupported ()

Tests if this input stream supports the mark and reset methods. This method simply performs in.markSupported().

Returns

• true if this stream type supports the mark and reset method; false otherwise.

See Also

• in
• InputStream.mark(int)
• InputStream.reset()

public int read ()

Reads the next byte of data from this input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

This method simply performs in.read() and returns the result.

Returns

• the next byte of data, or -1 if the end of the stream is reached.

Throws

IOException	if an I/O error occurs.

See Also

• in

public int read (byte[] b, int off, int len)

Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

This method simply performs in.read(b, off, len) and returns the result.

Parameters

b	the buffer into which the data is read.
off	the start offset in the destination array b
len	the maximum number of bytes read.

Returns

• the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Throws

NullPointerException	If b is null.
IndexOutOfBoundsException	If off is negative, len is negative, or len is greater than b.length - off
IOException	if an I/O error occurs.

See Also

• in

public int read (byte[] b)

Reads up to byte.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

This method simply performs the call read(b, 0, b.length) and returns the result. It is important that it does not do in.read(b) instead; certain subclasses of FilterInputStream depend on the implementation strategy actually used.

Parameters

b	the buffer into which the data is read.

Returns

• the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Throws

IOException	if an I/O error occurs.

See Also

• read(byte[], int, int)

public synchronized void reset ()

Repositions this stream to the position at the time the mark method was last called on this input stream.

This method simply performs in.reset().

Stream marks are intended to be used in situations where you need to read ahead a little to see what's in the stream. Often this is most easily done by invoking some general parser. If the stream is of the type handled by the parse, it just chugs along happily. If the stream is not of that type, the parser should toss an exception when it fails. If this happens within readlimit bytes, it allows the outer code to reset the stream and try another parser.

Throws

IOException	if the stream has not been marked or if the mark has been invalidated.

See Also

• in
• mark(int)

public long skip (long n)

Skips over and discards n bytes of data from the input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. The actual number of bytes skipped is returned.

This method simply performs in.skip(n).

Parameters

n	the number of bytes to be skipped.

Returns

• the actual number of bytes skipped.

Throws

IOException	if the stream does not support seek, or if some other I/O error occurs.