Java tutorial
/* * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code 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. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 in the LICENSE file that * accompanied this code). * * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.io; /** * Piped character-input streams. * * @author Mark Reinhold * @since 1.1 */ public class PipedReader extends Reader { boolean closedByWriter = false; boolean closedByReader = false; boolean connected = false; /* REMIND: 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. */ private static final int DEFAULT_PIPE_SIZE = 1024; /** * The circular buffer into which incoming data is placed. */ char buffer[]; /** * The index of the position in the circular buffer at which the * next character of data will be stored when received from the connected * piped writer. <code>in<0</code> implies the buffer is empty, * <code>in==out</code> implies the buffer is full */ int in = -1; /** * The index of the position in the circular buffer at which the next * character of data will be read by this piped reader. */ int out = 0; /** * Creates a <code>PipedReader</code> so * that it is connected to the piped writer * <code>src</code>. Data 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 PipedReader(PipedWriter src) throws IOException { this(src, DEFAULT_PIPE_SIZE); } /** * Creates a <code>PipedReader</code> so that it is connected * to the piped writer <code>src</code> and uses the specified * pipe size for the pipe's buffer. Data written to <code>src</code> * will then be available as input from this stream. * @param src the stream to connect to. * @param pipeSize the size of the pipe's buffer. * @exception IOException if an I/O error occurs. * @exception IllegalArgumentException if {@code pipeSize <= 0}. * @since 1.6 */ public PipedReader(PipedWriter src, int pipeSize) throws IOException { initPipe(pipeSize); connect(src); } /** * Creates a <code>PipedReader</code> so * that it is not yet {@linkplain #connect(java.io.PipedWriter) * connected}. It must be {@linkplain java.io.PipedWriter#connect( * java.io.PipedReader) connected} to a <code>PipedWriter</code> * before being used. */ public PipedReader() { initPipe(DEFAULT_PIPE_SIZE); } /** * Creates a <code>PipedReader</code> so that it is not yet * {@link #connect(java.io.PipedWriter) connected} and uses * the specified pipe size for the pipe's buffer. * It must be {@linkplain java.io.PipedWriter#connect( * java.io.PipedReader) connected} to a <code>PipedWriter</code> * before being used. * * @param pipeSize the size of the pipe's buffer. * @exception IllegalArgumentException if {@code pipeSize <= 0}. * @since 1.6 */ public PipedReader(int pipeSize) { initPipe(pipeSize); } private void initPipe(int pipeSize) { if (pipeSize <= 0) { throw new IllegalArgumentException("Pipe size <= 0"); } buffer = new char[pipeSize]; } /** * Causes this piped reader to be connected * to the piped writer <code>src</code>. * If this object is already connected to some * other piped writer, an <code>IOException</code> * is thrown. * <p> * If <code>src</code> is an * unconnected piped writer and <code>snk</code> * is an unconnected piped reader, they * may be connected by either the call: * * <pre><code>snk.connect(src)</code> </pre> * <p> * or the call: * * <pre><code>src.connect(snk)</code> </pre> * <p> * The two calls have the same effect. * * @param src The piped writer to connect to. * @exception IOException if an I/O error occurs. */ public void connect(PipedWriter src) throws IOException { src.connect(this); } /** * Receives a char of data. This method will block if no input is * available. */ synchronized void receive(int c) 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++] = (char) c; if (in >= buffer.length) { in = 0; } } /** * Receives data into an array of characters. This method will * block until some input is available. */ synchronized void receive(char c[], int off, int len) throws IOException { while (--len >= 0) { receive(c[off++]); } } /** * Notifies all waiting threads that the last character of data has been * received. */ synchronized void receivedLast() { closedByWriter = true; notifyAll(); } /** * Reads the next character of data from this piped stream. * If no character 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. * * @return the next character of data, or <code>-1</code> if the end of the * stream is reached. * @exception IOException if the pipe is * <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>, * {@link #connect(java.io.PipedWriter) unconnected}, closed, * or an I/O error occurs. */ 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++]; if (out >= buffer.length) { out = 0; } if (in == out) { /* now empty */ in = -1; } return ret; } /** * Reads up to <code>len</code> characters of data from this piped * stream into an array of characters. Less than <code>len</code> characters * will be read if the end of the data stream is reached or if * <code>len</code> exceeds the pipe's buffer size. This method * blocks until at least one character of input is available. * * @param cbuf the buffer into which the data is read. * @param off the start offset of the data. * @param len the maximum number of characters read. * @return the total number of characters 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 the pipe is * <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>, * {@link #connect(java.io.PipedWriter) unconnected}, closed, * or an I/O error occurs. * @exception IndexOutOfBoundsException {@inheritDoc} */ public synchronized int read(char cbuf[], int off, int len) 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"); } if ((off < 0) || (off > cbuf.length) || (len < 0) || ((off + len) > cbuf.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; } cbuf[off] = (char) c; int rlen = 1; while ((in >= 0) && (--len > 0)) { cbuf[off + rlen] = buffer[out++]; rlen++; if (out >= buffer.length) { out = 0; } if (in == out) { /* now empty */ in = -1; } } return rlen; } /** * Tell whether this stream is ready to be read. A piped character * stream is ready if the circular buffer is not empty. * * @exception IOException if the pipe is * <a href=PipedInputStream.html#BROKEN> <code>broken</code></a>, * {@link #connect(java.io.PipedWriter) unconnected}, or closed. */ public synchronized boolean ready() 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"); } if (in < 0) { return false; } else { return true; } } /** * Closes this piped 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; } }