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322 lines
11 KiB
Java
322 lines
11 KiB
Java
/* PushbackInputStream.java -- An input stream that can unread bytes
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Copyright (C) 1998, 1999, 2001, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.io;
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/**
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* This subclass of <code>FilterInputStream</code> provides the ability to
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* unread data from a stream. It maintains an internal buffer of unread
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* data that is supplied to the next read operation. This is conceptually
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* similar to mark/reset functionality, except that in this case the
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* position to reset the stream to does not need to be known in advance.
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* <p>
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* The default pushback buffer size one byte, but this can be overridden
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* by the creator of the stream.
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* <p>
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*
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* @author Aaron M. Renn (arenn@urbanophile.com)
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* @author Warren Levy <warrenl@cygnus.com>
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*/
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public class PushbackInputStream extends FilterInputStream
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{
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/**
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* This is the default buffer size
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*/
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private static final int DEFAULT_BUFFER_SIZE = 1;
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/**
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* This is the buffer that is used to store the pushed back data
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*/
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protected byte[] buf;
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/**
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* This is the position in the buffer from which the next byte will be
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* read. Bytes are stored in reverse order in the buffer, starting from
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* <code>buf[buf.length - 1]</code> to <code>buf[0]</code>. Thus when
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* <code>pos</code> is 0 the buffer is full and <code>buf.length</code> when
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* it is empty
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*/
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protected int pos;
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/**
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* This method initializes a <code>PushbackInputStream</code> to
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* read from the * specified subordinate <code>InputStream</code>
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* with a default pushback buffer * size of 1.
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*
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* @param in The subordinate stream to read from
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*/
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public PushbackInputStream(InputStream in)
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{
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this(in, DEFAULT_BUFFER_SIZE);
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}
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/**
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* This method initializes a <code>PushbackInputStream</code> to
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* read from the specified subordinate <code>InputStream</code> with
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* the specified buffer size
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*
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* @param in The subordinate <code>InputStream</code> to read from
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* @param size The pushback buffer size to use
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*/
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public PushbackInputStream(InputStream in, int size)
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{
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super(in);
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if (size < 0)
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throw new IllegalArgumentException();
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buf = new byte[size];
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pos = buf.length;
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}
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/**
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* This method returns the number of bytes that can be read from this
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* stream before a read can block. A return of 0 indicates that blocking
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* might (or might not) occur on the very next read attempt.
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* <p>
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* This method will return the number of bytes available from the
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* pushback buffer plus the number of bytes available from the
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* underlying stream.
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*
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* @return The number of bytes that can be read before blocking could occur
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*
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* @exception IOException If an error occurs
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*/
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public int available() throws IOException
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{
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return pos + super.available();
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}
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/**
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* This method closes the stream and releases any associated resources.
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*
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* @exception IOException If an error occurs.
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*/
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public synchronized void close() throws IOException
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{
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buf = null;
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super.close();
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}
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/**
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* This method returns <code>false</code> to indicate that it does
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* not support mark/reset functionality.
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*
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* @return This method returns <code>false</code> to indicate that
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* this class does not support mark/reset functionality
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*/
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public boolean markSupported()
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{
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return false;
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}
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/**
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* This method always throws an IOException in this class because
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* mark/reset functionality is not supported.
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*
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* @exception IOException Always thrown for this class
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*/
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public void reset() throws IOException
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{
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throw new IOException("Mark not supported in this class");
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}
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/**
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* This method reads an unsigned byte from the input stream and returns it
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* as an int in the range of 0-255. This method also will return -1 if
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* the end of the stream has been reached. The byte returned will be read
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* from the pushback buffer, unless the buffer is empty, in which case
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* the byte will be read from the underlying stream.
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* <p>
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* This method will block until the byte can be read.
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*
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* @return The byte read or -1 if end of stream
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*
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* @exception IOException If an error occurs
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*/
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public synchronized int read() throws IOException
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{
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if (pos < buf.length)
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return ((int) buf[pos++]) & 0xFF;
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return super.read();
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}
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/**
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* This method read bytes from a stream and stores them into a
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* caller supplied buffer. It starts storing the data at index
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* <code>offset</code> into the buffer and attempts to read
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* <code>len</code> bytes. This method can return before reading the
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* number of bytes requested. The actual number of bytes read is
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* returned as an int. A -1 is returned to indicate the end of the
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* stream.
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* <p>
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* This method will block until some data can be read.
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* <p>
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* This method first reads bytes from the pushback buffer in order to
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* satisfy the read request. If the pushback buffer cannot provide all
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* of the bytes requested, the remaining bytes are read from the
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* underlying stream.
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*
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* @param b The array into which the bytes read should be stored
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* @param off The offset into the array to start storing bytes
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* @param len The requested number of bytes to read
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*
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* @return The actual number of bytes read, or -1 if end of stream.
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*
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* @exception IOException If an error occurs.
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*/
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public synchronized int read(byte[] b, int off, int len) throws IOException
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{
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if (off < 0 || len < 0 || off + len > b.length)
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throw new ArrayIndexOutOfBoundsException();
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int numBytes = Math.min(buf.length - pos, len);
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if (numBytes > 0)
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{
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System.arraycopy (buf, pos, b, off, numBytes);
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pos += numBytes;
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return numBytes;
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}
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return super.read(b, off, len);
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}
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/**
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* This method pushes a single byte of data into the pushback buffer.
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* The byte pushed back is the one that will be returned as the first byte
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* of the next read.
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* <p>
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* If the pushback buffer is full, this method throws an exception.
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* <p>
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* The argument to this method is an <code>int</code>. Only the low
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* eight bits of this value are pushed back.
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*
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* @param b The byte to be pushed back, passed as an int
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*
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* @exception IOException If the pushback buffer is full.
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*/
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public synchronized void unread(int b) throws IOException
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{
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if (pos <= 0)
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throw new IOException("Insufficient space in pushback buffer");
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buf[--pos] = (byte) b;
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}
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/**
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* This method pushes all of the bytes in the passed byte array into
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* the pushback bfer. These bytes are pushed in reverse order so that
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* the next byte read from the stream after this operation will be
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* <code>b[0]</code> followed by <code>b[1]</code>, etc.
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* <p>
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* If the pushback buffer cannot hold all of the requested bytes, an
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* exception is thrown.
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*
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* @param b The byte array to be pushed back
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*
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* @exception IOException If the pushback buffer is full
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*/
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public synchronized void unread(byte[] b) throws IOException
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{
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unread(b, 0, b.length);
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}
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/**
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* This method pushed back bytes from the passed in array into the
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* pushback buffer. The bytes from <code>b[offset]</code> to
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* <cdoe>b[offset + len]</code> are pushed in reverse order so that
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* the next byte read from the stream after this operation will be
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* <code>b[offset]</code> followed by <code>b[offset + 1]</code>,
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* etc.
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* <p>
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* If the pushback buffer cannot hold all of the requested bytes, an
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* exception is thrown.
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*
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* @param b The byte array to be pushed back
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* @param off The index into the array where the bytes to be push start
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* @param len The number of bytes to be pushed.
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*
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* @exception IOException If the pushback buffer is full
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*/
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public synchronized void unread(byte[] b, int off, int len)
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throws IOException
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{
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if (pos < len)
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throw new IOException("Insufficient space in pushback buffer");
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// Note the order that these bytes are being added is the opposite
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// of what would be done if they were added to the buffer one at a time.
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// See the Java Class Libraries book p. 1390.
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System.arraycopy(b, off, buf, pos - len, len);
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// Don't put this into the arraycopy above, an exception might be thrown
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// and in that case we don't want to modify pos.
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pos -= len;
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}
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/**
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* This method skips the specified number of bytes in the stream. It
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* returns the actual number of bytes skipped, which may be less than the
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* requested amount.
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* <p>
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* This method first discards bytes from the buffer, then calls the
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* <code>skip</code> method on the underlying <code>InputStream</code> to
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* skip additional bytes if necessary.
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*
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* @param num_bytes The requested number of bytes to skip
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*
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* @return The actual number of bytes skipped.
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*
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* @exception IOException If an error occurs
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*
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* @since 1.2
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*/
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public synchronized long skip(long n) throws IOException
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{
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final long origN = n;
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if (n > 0L)
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{
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int numread = (int) Math.min((long) (buf.length - pos), n);
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pos += numread;
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n -= numread;
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n -= super.skip(n);
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}
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return origN - n;
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}
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}
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