/*
* @(#)PushbackInputStream.java 1.39 06/10/10
*
* Copyright 1990-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version
* 2 only, as published by the Free Software Foundation.
*
* This program 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 version 2 for more details (a copy is
* included at /legal/license.txt).
*
* You should have received a copy of the GNU General Public License
* version 2 along with this work; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 or visit www.sun.com if you need additional
* information or have any questions.
*
*/
package java.io;
/**
* A <code>PushbackInputStream</code> adds
* functionality to another input stream, namely
* the ability to "push back" or "unread"
* one byte. This is useful in situations where
* it is convenient for a fragment of code
* to read an indefinite number of data bytes
* that are delimited by a particular byte
* value; after reading the terminating byte,
* the code fragment can "unread" it, so that
* the next read operation on the input stream
* will reread the byte that was pushed back.
* For example, bytes representing the characters
* constituting an identifier might be terminated
* by a byte representing an operator character;
* a method whose job is to read just an identifier
* can read until it sees the operator and
* then push the operator back to be re-read.
*
* @version 1.31, 02/02/00
* @since JDK1.0
*/
public
class PushbackInputStream extends FilterInputStream {
/**
* The pushback buffer.
* @since JDK1.1
*/
protected byte[] buf;
/**
* The position within the pushback buffer from which the next byte will
* be read. When the buffer is empty, <code>pos</code> is equal to
* <code>buf.length</code>; when the buffer is full, <code>pos</code> is
* equal to zero.
*
* @since JDK1.1
*/
protected int pos;
/**
* Check to make sure that this stream has not been closed
*/
private void ensureOpen() throws IOException {
if (in == null)
throw new IOException("Stream closed");
}
/**
* Creates a <code>PushbackInputStream</code>
* with a pushback buffer of the specified <code>size</code>,
* and saves its argument, the input stream
* <code>in</code>, for later use. Initially,
* there is no pushed-back byte (the field
* <code>pushBack</code> is initialized to
* <code>-1</code>).
*
* @param in the input stream from which bytes will be read.
* @param size the size of the pushback buffer.
* @exception IllegalArgumentException if size is <= 0
* @since JDK1.1
*/
public PushbackInputStream(InputStream in, int size) {
super(in);
if (size <= 0) {
throw new IllegalArgumentException("size <= 0");
}
this.buf = new byte[size];
this.pos = size;
}
/**
* Creates a <code>PushbackInputStream</code>
* and saves its argument, the input stream
* <code>in</code>, for later use. Initially,
* there is no pushed-back byte (the field
* <code>pushBack</code> is initialized to
* <code>-1</code>).
*
* @param in the input stream from which bytes will be read.
*/
public PushbackInputStream(InputStream in) {
this(in, 1);
}
/**
* Reads the next byte of data from this input stream. The value
* byte is returned as an <code>int</code> in the range
* <code>0</code> to <code>255</code>. If no byte is available
* because the end of the stream has been reached, the value
* <code>-1</code> is returned. This method blocks until input data
* is available, the end of the stream is detected, or an exception
* is thrown.
*
* <p> This method returns the most recently pushed-back byte, if there is
* one, and otherwise calls the <code>read</code> method of its underlying
* input stream and returns whatever value that method returns.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read()
*/
public int read() throws IOException {
ensureOpen();
if (pos < buf.length) {
return buf[pos++] & 0xff;
}
return super.read();
}
/**
* Reads up to <code>len</code> bytes of data from this input stream into
* an array of bytes. This method first reads any pushed-back bytes; after
* that, if fewer than than <code>len</code> bytes have been read then it
* reads from the underlying input stream. This method blocks until at
* least 1 byte of input is available.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data.
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read(byte[], int, int)
*/
public int read(byte[] b, int off, int len) throws IOException {
ensureOpen();
if ((off < 0) || (off > b.length) || (len < 0) ||
((off + len) > b.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
}
if (len == 0) {
return 0;
}
int avail = buf.length - pos;
if (avail > 0) {
if (len < avail) {
avail = len;
}
System.arraycopy(buf, pos, b, off, avail);
pos += avail;
off += avail;
len -= avail;
}
if (len > 0) {
len = super.read(b, off, len);
if (len == -1) {
return avail == 0 ? -1 : avail;
}
return avail + len;
}
return avail;
}
/**
* Pushes back a byte by copying it to the front of the pushback buffer.
* After this method returns, the next byte to be read will have the value
* <code>(byte)b</code>.
*
* @param b the <code>int</code> value whose low-order
* byte is to be pushed back.
* @exception IOException If there is not enough room in the pushback
* buffer for the byte.
*/
public void unread(int b) throws IOException {
ensureOpen();
if (pos == 0) {
throw new IOException("Push back buffer is full");
}
buf[--pos] = (byte)b;
}
/**
* Pushes back a portion of an array of bytes by copying it to the front
* of the pushback buffer. After this method returns, the next byte to be
* read will have the value <code>b[off]</code>, the byte after that will
* have the value <code>b[off+1]</code>, and so forth.
*
* @param b the byte array to push back.
* @param off the start offset of the data.
* @param len the number of bytes to push back.
* @exception IOException If there is not enough room in the pushback
* buffer for the specified number of bytes.
* @since JDK1.1
*/
public void unread(byte[] b, int off, int len) throws IOException {
ensureOpen();
if (len > pos) {
throw new IOException("Push back buffer is full");
}
pos -= len;
System.arraycopy(b, off, buf, pos, len);
}
/**
* Pushes back an array of bytes by copying it to the front of the
* pushback buffer. After this method returns, the next byte to be read
* will have the value <code>b[0]</code>, the byte after that will have the
* value <code>b[1]</code>, and so forth.
*
* @param b the byte array to push back
* @exception IOException If there is not enough room in the pushback
* buffer for the specified number of bytes.
* @since JDK1.1
*/
public void unread(byte[] b) throws IOException {
unread(b, 0, b.length);
}
/**
* Returns the number of bytes that can be read from this input stream
* without blocking. This method calls the <code>available</code> method
* of the underlying input stream; it returns that value plus the number of
* bytes that have been pushed back.
*
* @return the number of bytes that can be read from the input stream
* without blocking.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
* @see java.io.InputStream#available()
*/
public int available() throws IOException {
ensureOpen();
return (buf.length - pos) + super.available();
}
/**
* Skips over and discards <code>n</code> bytes of data from this
* input stream. The <code>skip</code> method may, for a variety of
* reasons, end up skipping over some smaller number of bytes,
* possibly zero. If <code>n</code> is negative, no bytes are skipped.
*
* <p> The <code>skip</code> method of <code>PushbackInputStream</code>
* first skips over the bytes in the pushback buffer, if any. It then
* calls the <code>skip</code> method of the underlying input stream if
* more bytes need to be skipped. The actual number of bytes skipped
* is returned.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
* @see java.io.InputStream#skip(long n)
* @since 1.2
*/
public long skip(long n) throws IOException {
ensureOpen();
if (n <= 0) {
return 0;
}
long pskip = buf.length - pos;
if (pskip > 0) {
if (n < pskip) {
pskip = n;
}
pos += pskip;
n -= pskip;
}
if (n > 0) {
pskip += super.skip(n);
}
return pskip;
}
/**
* Tests if this input stream supports the <code>mark</code> and
* <code>reset</code> methods, which it does not.
*
* @return <code>false</code>, since this class does not support the
* <code>mark</code> and <code>reset</code> methods.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return false;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
*
* @exception IOException if an I/O error occurs.
*/
public synchronized void close() throws IOException {
if (in == null)
return;
in.close();
in = null;
buf = null;
}
}