java.io

Class PushbackInputStream

Implemented Interfaces:
AutoCloseable, Closeable

public class PushbackInputStream
extends FilterInputStream

This subclass of FilterInputStream provides the ability to unread data from a stream. It maintains an internal buffer of unread data that is supplied to the next read operation. This is conceptually similar to mark/reset functionality, except that in this case the position to reset the stream to does not need to be known in advance.

The default pushback buffer size one byte, but this can be overridden by the creator of the stream.

Field Summary

protected byte[]
buf
This is the buffer that is used to store the pushed back data
protected int
pos
This is the position in the buffer from which the next byte will be read.

Fields inherited from class java.io.FilterInputStream

in

Constructor Summary

PushbackInputStream(InputStream in)
This method initializes a PushbackInputStream to read from the specified subordinate InputStream with a default pushback buffer size of 1.
PushbackInputStream(InputStream in, int size)
This method initializes a PushbackInputStream to read from the specified subordinate InputStream with the specified buffer size

Method Summary

int
available()
This method returns the number of bytes that can be read from this stream before a read can block.
void
close()
This method closes the stream and releases any associated resources.
boolean
markSupported()
This method returns false to indicate that it does not support mark/reset functionality.
int
read()
This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255.
int
read(byte[] b, int off, int len)
This method read bytes from a stream and stores them into a caller supplied buffer.
void
reset()
This method always throws an IOException in this class because mark/reset functionality is not supported.
long
skip(long n)
This method skips the specified number of bytes in the stream.
void
unread(byte[] b)
This method pushes all of the bytes in the passed byte array into the pushback bfer.
void
unread(byte[] b, int off, int len)
This method pushed back bytes from the passed in array into the pushback buffer.
void
unread(int b)
This method pushes a single byte of data into the pushback buffer.

Methods inherited from class java.io.FilterInputStream

available, close, mark, markSupported, read, read, read, reset, skip

Methods inherited from class java.io.InputStream

available, close, mark, markSupported, read, read, read, reset, skip

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

buf

protected byte[] buf
This is the buffer that is used to store the pushed back data

pos

protected int pos
This is the position in the buffer from which the next byte will be read. Bytes are stored in reverse order in the buffer, starting from buf[buf.length - 1] to buf[0]. Thus when pos is 0 the buffer is full and buf.length when it is empty

Constructor Details

PushbackInputStream

public PushbackInputStream(InputStream in)
This method initializes a PushbackInputStream to read from the specified subordinate InputStream with a default pushback buffer size of 1.
Parameters:
in - The subordinate stream to read from

PushbackInputStream

public PushbackInputStream(InputStream in,
                           int size)
This method initializes a PushbackInputStream to read from the specified subordinate InputStream with the specified buffer size
Parameters:
in - The subordinate InputStream to read from
size - The pushback buffer size to use

Method Details

available

public int available()
            throws IOException
This method returns the number of bytes that can be read from this stream before a read can block. A return of 0 indicates that blocking might (or might not) occur on the very next read attempt.

This method will return the number of bytes available from the pushback buffer plus the number of bytes available from the underlying stream.

Overrides:
available in interface FilterInputStream
Returns:
The number of bytes that can be read before blocking could occur
Throws:
IOException - If an error occurs

close

public void close()
            throws IOException
This method closes the stream and releases any associated resources.
Specified by:
close in interface Closeable
close in interface AutoCloseable
Overrides:
close in interface FilterInputStream
Throws:
IOException - If an error occurs.

markSupported

public boolean markSupported()
This method returns false to indicate that it does not support mark/reset functionality.
Overrides:
markSupported in interface FilterInputStream
Returns:
This method returns false to indicate that this class does not support mark/reset functionality

read

public int read()
            throws IOException
This method reads an unsigned byte from the input stream and returns it as an int in the range of 0-255. This method also will return -1 if the end of the stream has been reached. The byte returned will be read from the pushback buffer, unless the buffer is empty, in which case the byte will be read from the underlying stream.

This method will block until the byte can be read.

Overrides:
read in interface FilterInputStream
Returns:
The byte read or -1 if end of stream
Throws:
IOException - If an error occurs

read

public int read(byte[] b,
                int off,
                int len)
            throws IOException
This method read bytes from a stream and stores them into a caller supplied buffer. It starts storing the data at index offset into the buffer and attempts to read len bytes. This method can return before reading the number of bytes requested. The actual number of bytes read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method first reads bytes from the pushback buffer in order to satisfy the read request. If the pushback buffer cannot provide all of the bytes requested, the remaining bytes are read from the underlying stream.

Overrides:
read in interface FilterInputStream
Parameters:
b - The array into which the bytes read should be stored
off - The offset into the array to start storing bytes
len - The requested number of bytes to read
Returns:
The actual number of bytes read, or -1 if end of stream.
Throws:
IOException - If an error occurs.

reset

public void reset()
            throws IOException
This method always throws an IOException in this class because mark/reset functionality is not supported.
Overrides:
reset in interface FilterInputStream
Throws:
IOException - Always thrown for this class

skip

public long skip(long n)
            throws IOException
This method skips the specified number of bytes in the stream. It returns the actual number of bytes skipped, which may be less than the requested amount.

This method first discards bytes from the buffer, then calls the skip method on the underlying InputStream to skip additional bytes if necessary.

Overrides:
skip in interface FilterInputStream
Parameters:
n - The requested number of bytes to skip
Returns:
The actual number of bytes skipped.
Throws:
IOException - If an error occurs
Since:
1.2

unread

public void unread(byte[] b)
            throws IOException
This method pushes all of the bytes in the passed byte array into the pushback bfer. These bytes are pushed in reverse order so that the next byte read from the stream after this operation will be b[0] followed by b[1], etc.

If the pushback buffer cannot hold all of the requested bytes, an exception is thrown.

Parameters:
b - The byte array to be pushed back
Throws:
IOException - If the pushback buffer is full

unread

public void unread(byte[] b,
                   int off,
                   int len)
            throws IOException
This method pushed back bytes from the passed in array into the pushback buffer. The bytes from b[offset] to b[offset + len] are pushed in reverse order so that the next byte read from the stream after this operation will be b[offset] followed by b[offset + 1], etc.

If the pushback buffer cannot hold all of the requested bytes, an exception is thrown.

Parameters:
b - The byte array to be pushed back
off - The index into the array where the bytes to be push start
len - The number of bytes to be pushed.
Throws:
IOException - If the pushback buffer is full

unread

public void unread(int b)
            throws IOException
This method pushes a single byte of data into the pushback buffer. The byte pushed back is the one that will be returned as the first byte of the next read.

If the pushback buffer is full, this method throws an exception.

The argument to this method is an int. Only the low eight bits of this value are pushed back.

Parameters:
b - The byte to be pushed back, passed as an int
Throws:
IOException - If the pushback buffer is full.

PushbackInputStream.java -- An input stream that can unread bytes Copyright (C) 1998, 1999, 2001, 2002, 2005 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.