字符管道流(线程流)——PipedReader、PipedWriter
字符管道流(线程流)——PipedReader、PipedWriter。管道流（线程流）的升级版！，主要用途也是在线程间通讯，不过这个可以用来传输字符；具体可以参考管道流(线程流)——PipedInputStream、PipedOutputStream。这里就不做演示了，以下是字符管道流源码：
PipedReader：
/*
* Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.io;
/**
* Piped character-input streams.
*
* @author Mark Reinhold
* @since JDK1.1
*/
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. in<0 implies the buffer is empty,
* in==out 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 PipedReader so
* that it is connected to the piped writer
* src. Data written to src
* 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 PipedReader so that it is connected
* to the piped writer src and uses the specified
* pipe size for the pipe's buffer. Data written to src
* 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 PipedReader 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 PipedWriter
* before being used.
*/
public PipedReader() {
initPipe(DEFAULT_PIPE_SIZE);
}
/**
* Creates a PipedReader 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 PipedWriter
* 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 src.
* If this object is already connected to some
* other piped writer, an IOException
* is thrown.
*
* If src is an
* unconnected piped writer and snk
* is an unconnected piped reader, they
* may be connected by either the call:
*
*
snk.connect(src)
*
* or the call:
*
*
src.connect(snk)
*
* 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 -1 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 -1 if the end of the
* stream is reached.
* @exception IOException if the pipe is
* broken,
* {@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 len characters of data from this piped
* stream into an array of characters. Less than len characters
* will be read if the end of the data stream is reached or if
* len 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
* -1 if there is no more data because the end of
* the stream has been reached.
* @exception IOException if the pipe is
* broken,
* {@link #connect(java.io.PipedWriter) unconnected}, closed,
* or an I/O error occurs.
*/
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
* broken,
* {@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;
}
}
PipedWriter：
/*
* Copyright (c) 1996, 2006, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.io;
/**
* Piped character-output streams.
*
* @author Mark Reinhold
* @since JDK1.1
*/
public class PipedWriter extends Writer {
/* 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). */
private PipedReader sink;
/* This flag records the open status of this particular writer. It
* is independent of the status flags defined in PipedReader. It is
* used to do a sanity check on connect.
*/
private boolean closed = false;
/**
* Creates a piped writer connected to the specified piped
* reader. Data characters written to this stream will then be
* available as input from snk.
*
* @param snk The piped reader to connect to.
* @exception IOException if an I/O error occurs.
*/
public PipedWriter(PipedReader snk) throws IOException {
connect(snk);
}
/**
* Creates a piped writer that is not yet connected to a
* piped reader. It must be connected to a piped reader,
* either by the receiver or the sender, before being used.
*
* @see java.io.PipedReader#connect(java.io.PipedWriter)
* @see java.io.PipedWriter#connect(java.io.PipedReader)
*/
public PipedWriter() {
}
/**
* Connects this piped writer to a receiver. If this object
* is already connected to some other piped reader, an
* IOException is thrown.
*
* If snk is an unconnected piped reader and
* src is an unconnected piped writer, they may
* be connected by either the call:
*
* src.connect(snk)
* or the call:
*
* snk.connect(src)
* The two calls have the same effect.
*
* @param snk the piped reader to connect to.
* @exception IOException if an I/O error occurs.
*/
public synchronized void connect(PipedReader snk) throws IOException {
if (snk == null) {
throw new NullPointerException();
} else if (sink != null || snk.connected) {
throw new IOException("Already connected");
} else if (snk.closedByReader || closed) {
throw new IOException("Pipe closed");
}
sink = snk;
snk.in = -1;
snk.out = 0;
snk.connected = true;
}
/**
* Writes the specified char to the piped output stream.
* If a thread was reading data characters from the connected piped input
* stream, but the thread is no longer alive, then an
* IOException is thrown.
*
* Implements the write method of Writer.
*
* @param c the char to be written.
* @exception IOException if the pipe is
* broken,
* {@link #connect(java.io.PipedReader) unconnected}, closed
* or an I/O error occurs.
*/
public void write(int c) throws IOException {
if (sink == null) {
throw new IOException("Pipe not connected");
}
sink.receive(c);
}
/**
* Writes len characters from the specified character array
* starting at offset off to this piped output stream.
* This method blocks until all the characters are written to the output
* stream.
* If a thread was reading data characters from the connected piped input
* stream, but the thread is no longer alive, then an
* IOException is thrown.
*
* @param cbuf the data.
* @param off the start offset in the data.
* @param len the number of characters to write.
* @exception IOException if the pipe is
* broken,
* {@link #connect(java.io.PipedReader) unconnected}, closed
* or an I/O error occurs.
*/
public void write(char cbuf[], int off, int len) throws IOException {
if (sink == null) {
throw new IOException("Pipe not connected");
} else if ((off | len | (off + len) | (cbuf.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
}
sink.receive(cbuf, off, len);
}
/**
* Flushes this output stream and forces any buffered output characters
* to be written out.
* This will notify any readers that characters are waiting in the pipe.
*
* @exception IOException if the pipe is closed, or an I/O error occurs.
*/
public synchronized void flush() throws IOException {
if (sink != null) {
if (sink.closedByReader || closed) {
throw new IOException("Pipe closed");
}
synchronized (sink) {
sink.notifyAll();
}
}
}
/**
* Closes this piped output stream and releases any system resources
* associated with this stream. This stream may no longer be used for
* writing characters.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {
closed = true;
if (sink != null) {
sink.receivedLast();
}
}
}