pipedinputstream.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 346 行

/*
 * @(#)PipedInputStream.java	1.38 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 piped input stream should be connected
 * to a piped output stream; the piped  input
 * stream then provides whatever data bytes
 * are written to the piped output  stream.
 * Typically, data is read from a <code>PipedInputStream</code>
 * object by one thread  and data is written
 * to the corresponding <code>PipedOutputStream</code>
 * by some  other thread. Attempting to use
 * both objects from a single thread is not
 * recommended, as it may deadlock the thread.
 * The piped input stream contains a buffer,
 * decoupling read operations from write operations,
 * within limits.
 *
 * @author  James Gosling
 * @version 1.30, 02/02/00
 * @see     java.io.PipedOutputStream
 * @since   JDK1.0
 */
public
class PipedInputStream extends InputStream {
    boolean closedByWriter = false;
    boolean closedByReader = false;
    boolean connected = false;

	/* NOTE: identification of the read and write sides needs to be
	   more sophisticated.  Either using thread groups (but what about
	   pipes within a thread?) or using finalization (but it may be a
	   long time until the next GC). */
    Thread readSide;
    Thread writeSide;

    /**
     * The size of the pipe's circular input buffer.
     * @since   JDK1.1
     */
    protected static final int PIPE_SIZE = 1024;

    /**
     * The circular buffer into which incoming data is placed.
     * @since   JDK1.1
     */
    protected byte buffer[] = new byte[PIPE_SIZE];

    /**
     * The index of the position in the circular buffer at which the
     * next byte of data will be stored when received from the connected
     * piped output stream. <code>in&lt;0</code> implies the buffer is empty,
     * <code>in==out</code> implies the buffer is full
     * @since   JDK1.1
     */
    protected int in = -1;

    /**
     * The index of the position in the circular buffer at which the next
     * byte of data will be read by this piped input stream.
     * @since   JDK1.1
     */
    protected int out = 0;

    /**
     * Creates a <code>PipedInputStream</code> so
     * that it is connected to the piped output
     * stream <code>src</code>. Data bytes written
     * to <code>src</code> will then be  available
     * as input from this stream.
     *
     * @param      src   the stream to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public PipedInputStream(PipedOutputStream src) throws IOException {
	connect(src);
    }

    /**
     * Creates a <code>PipedInputStream</code> so
     * that it is not  yet connected. It must be
     * connected to a <code>PipedOutputStream</code>
     * before being used.
     *
     * @see     java.io.PipedInputStream#connect(java.io.PipedOutputStream)
     * @see     java.io.PipedOutputStream#connect(java.io.PipedInputStream)
     */
    public PipedInputStream() {
    }

    /**
     * Causes this piped input stream to be connected
     * to the piped  output stream <code>src</code>.
     * If this object is already connected to some
     * other piped output  stream, an <code>IOException</code>
     * is thrown.
     * <p>
     * If <code>src</code> is an
     * unconnected piped output stream and <code>snk</code>
     * is an unconnected piped input stream, they
     * may be connected by either the call:
     * <p>
     * <pre><code>snk.connect(src)</code> </pre>
     * <p>
     * or the call:
     * <p>
     * <pre><code>src.connect(snk)</code> </pre>
     * <p>
     * The two
     * calls have the same effect.
     *
     * @param      src   The piped output stream to connect to.
     * @exception  IOException  if an I/O error occurs.
     */
    public void connect(PipedOutputStream src) throws IOException {
	src.connect(this);
    }

    /**
     * Receives a byte of data.  This method will block if no input is
     * available.
     * @param b the byte being received
     * @exception IOException If the pipe is broken.
     * @since     JDK1.1
     */
    protected synchronized void receive(int b) throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByWriter || closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (readSide != null && !readSide.isAlive()) {
            throw new IOException("Read end dead");
        }

	writeSide = Thread.currentThread();
	while (in == out) {
	    if ((readSide != null) && !readSide.isAlive()) {
		throw new IOException("Pipe broken");
	    }
	    /* full: kick any waiting readers */
	    notifyAll();
	    try {
	        wait(1000);
	    } catch (InterruptedException ex) {
		throw new java.io.InterruptedIOException();
	    }
	}
	if (in < 0) {
	    in = 0;
	    out = 0;
	}
	buffer[in++] = (byte)(b & 0xFF);
	if (in >= buffer.length) {
	    in = 0;
	}
    }

    /**
     * Receives data into an array of bytes.  This method will
     * block until some input is available.
     * @param b the buffer into which the data is received
     * @param off the start offset of the data
     * @param len the maximum number of bytes received
     * @return the actual number of bytes received, -1 is
     *          returned when the end of the stream is reached.
     * @exception IOException If an I/O error has occurred.
     */
    synchronized void receive(byte b[], int off, int len)  throws IOException {
	while (--len >= 0) {
	    receive(b[off++]);
	}
    }

    /**
     * Notifies all waiting threads that the last byte of data has been
     * received.
     */
    synchronized void receivedLast() {
	closedByWriter = true;
	notifyAll();
    }

    /**
     * Reads the next byte of data from this piped 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.
     * If a thread was providing data bytes
     * to the connected piped output stream, but
     * the  thread is no longer alive, then an
     * <code>IOException</code> is thrown.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if the pipe is broken.
     */
    public synchronized int read()  throws IOException {
        if (!connected) {
            throw new IOException("Pipe not connected");
        } else if (closedByReader) {
	    throw new IOException("Pipe closed");
	} else if (writeSide != null && !writeSide.isAlive()
                   && !closedByWriter && (in < 0)) {
            throw new IOException("Write end dead");
        }

        readSide = Thread.currentThread();
	int trials = 2;
	while (in < 0) {
	    if (closedByWriter) {
		/* closed by writer, return EOF */
		return -1;
	    }
	    if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
		throw new IOException("Pipe broken");
	    }
            /* might be a writer waiting */
	    notifyAll();
	    try {
	        wait(1000);
	    } catch (InterruptedException ex) {
		throw new java.io.InterruptedIOException();
	    }
 	}
	int ret = buffer[out++] & 0xFF;
	if (out >= buffer.length) {
	    out = 0;
	}
	if (in == out) {
            /* now empty */
	    in = -1;
	}
	return ret;
    }

    /**
     * Reads up to <code>len</code> bytes of data from this piped input
     * stream into an array of bytes. Less than <code>len</code> bytes
     * will be read if the end of the data stream is reached. This method
     * blocks until at least one byte of input is available.
     * If a thread was providing data bytes
     * to the connected piped output stream, but
     * the  thread is no longer alive, then an
     * <code>IOException</code> is thrown.
     *
     * @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.
     */
    public synchronized int read(byte b[], int off, int len)  throws IOException {
	if (b == null) {
	    throw new NullPointerException();
	} else if ((off < 0) || (off > b.length) || (len < 0) ||
		   ((off + len) > b.length) || ((off + len) < 0)) {
	    throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	    return 0;
	}

        /* possibly wait on the first character */
	int c = read();
	if (c < 0) {
	    return -1;
	}
	b[off] = (byte) c;
	int rlen = 1;
	while ((in >= 0) && (--len > 0)) {
	    b[off + rlen] = buffer[out++];
	    rlen++;
	    if (out >= buffer.length) {
		out = 0;
	    }
	    if (in == out) {
                /* now empty */
		in = -1;
	    }
	}
	return rlen;
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking. This method overrides the <code>available</code>
     * method of the parent class.
     *
     * @return     the number of bytes that can be read from this input stream
     *             without blocking.
     * @exception  IOException  if an I/O error occurs.
     * @since   JDK1.0.2
     */
  public synchronized int available() throws IOException {
    if(in < 0)
      return 0;
    else if(in == out)
      return buffer.length;
    else if (in > out)
      return in - out;
    else
      return in + buffer.length - out;
  }

    /**
     * Closes this piped input stream and releases any system resources
     * associated with the stream.
     *
     * @exception  IOException  if an I/O error occurs.
     */
    public void close()  throws IOException {
	in = -1;
	closedByReader = true;
    }
}