StreamConnector.java
/*
** Module : StreamConnector.java
** Abstract : connects two streams and forwards contents of one to the other
**
** Copyright (c) 2005-2022, Golden Code Development Corporation.
**
** -#- -I- --Date-- -T- --JPRM-- ----------------Description-----------------
** 001 GES 20050629 NEW @21567 Created initial version which provides a
** mechanism to connect two streams and
** forward the contents from one to the other.
** 002 GES 20060216 CHG @24668 Safer close semantics.
** 003 TJD 20220504 Java 11 compatibility minor changes
*/
/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** 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 Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
**
** Additional terms under GNU Affero GPL version 3 section 7:
**
** Under Section 7 of the GNU Affero GPL version 3, the following additional
** terms apply to the works covered under the License. These additional terms
** are non-permissive additional terms allowed under Section 7 of the GNU
** Affero GPL version 3 and may not be removed by you.
**
** 0. Attribution Requirement.
**
** You must preserve all legal notices or author attributions in the covered
** work or Appropriate Legal Notices displayed by works containing the covered
** work. You may not remove from the covered work any author or developer
** credit already included within the covered work.
**
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**
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** attribution required in this license.
*/
package com.goldencode.p2j.io;
import java.io.*;
/**
* General purpose service that connects two streams and forwards contents
* of the input stream to the output stream. The streams are specified by
* an <code>InputStream</code> and <code>OutputStream</code>.
* <p>
* Uses a worker thread to provide this service. The thread is created and
* started in the constructor. This thread copies data while data exists in
* the input stream and pauses in between tests of whether any data exists
* to be copied. This polling loop will continue until the close flag is
* raised (see {@link #close}) or there is an <code>IOException</code> or
* <code>InterruptedException</code> on the copy thread. The core
* implementation of the copying can be found in the {@link #run} method.
*
* @author GES
*/
public class StreamConnector
implements Runnable
{
/** Size of the byte array used for block copying. */
private static final int BUF_SIZE = 8192;
/** Milliseconds to sleep between polls of the input stream. */
private static final long SLEEP_INTERVAL = 256;
/** The input stream from which we read. */
private InputStream in = null;
/** The output stream to which we write. */
private OutputStream out = null;
/** An object on which the close operations are synchronized. */
private Object lock = new Object();
/** Specifies if the copy thread should exit when no data is left. */
private boolean flag = false;
/** If <code>true</code> the input stream should be closed on exit. */
private boolean closeIn = false;
/** If <code>true</code> the output stream should be closed on exit. */
private boolean closeOut = false;
/**
* Instantiates the connector and starts the copy thread that drives the
* transfer of data from the input stream to the output stream.
*
* @param in
* The input stream from which to read.
* @param out
* The output stream on which to write.
* @param closeIn
* If <code>true</code>, at exit the copy thread will close
* the input stream, otherwise the stream will not be closed.
* @param closeOut
* If <code>true</code>, at exit the copy thread will close
* the output stream, otherwise the stream will not be closed.
*/
public StreamConnector(InputStream in,
OutputStream out,
boolean closeIn,
boolean closeOut)
{
this.in = in;
this.out = out;
this.closeIn = closeIn;
this.closeOut = closeOut;
// create and start the thread that drives the copying
Thread t1 = new Thread(this);
t1.start();
}
/**
* Sets the close flag to trigger an exit by the copy thread when no data
* remains in the input stream.
*/
public void close()
{
synchronized (lock)
{
if (!flag)
{
flag = true;
try
{
lock.wait();
}
catch (InterruptedException ie)
{
// best efforts to wait only
}
}
}
}
/**
* Checks the state of the close flag. If <code>true</code>, the copy
* thread will close when no data remains in the input stream.
*/
public boolean isClosed()
{
boolean result = false;
synchronized (lock)
{
result = flag;
lock.notifyAll();
}
return result;
}
/**
* Copies data from the input stream to the output stream as long as
* the close flag is <code>false</code> or there is data to copy. On
* exit, the input and output streams are closed if and only if such a
* close was specified in the constructor. This method is called on a
* new thread which is instantiated in the constructor. This thread
* exits when this method is complete.
* <p>
* The copy algorithm is based on a block size specified by the member
* <code>BUF_SIZE</code>.
* <p>
* Please note that as of J2SE 1.4.x there are no facilities that provide
* non-blocking I/O for pipes used between processes. Both the original
* <code>java.io</code> and <code>java.nio</code> packages support pipes
* for use between 2 threads in the same JVM but DO NOT support the
* ability to set the ends of the pipe using pipes that are externally
* created. For this reason, this method uses a polling approach to
* the detection of available bytes. This allows the thread to drop out
* cleanly when the close flag is turned on, even in the case where no
* data has been written to the pipe in a long time. The polling interval
* is specified by the member <code>SLEEP_INTERVAL</code>.
*/
public void run()
{
byte[] buffer = new byte[BUF_SIZE];
try
{
// continue while there is data to copy but if there is no data
// AND the close flag is true, then we exit; note that the close
// flag is tested using a synchronized method to ensure thread
// safety
while (in.available() > 0 || !isClosed())
{
int num = in.available();
while (num > 0)
{
// read the data as a full block or the total amount avail
int obtained = in.read(buffer, 0, Math.min(num, BUF_SIZE));
// decrement our total remaining available bytes
num -= obtained;
// write the data to the output stream
out.write(buffer, 0, obtained);
}
Thread.sleep(SLEEP_INTERVAL);
}
}
catch (IOException ioe)
{
// exit silently
}
catch (InterruptedException ie)
{
// exit silently
}
finally
{
try
{
synchronized (lock)
{
// ensure that a close() called after this point is safe
if (!flag)
{
flag = true;
}
else
{
lock.notifyAll();
}
}
// close the input stream if requested
if (closeIn)
{
in.close();
}
// close the output stream if requested
if (closeOut)
{
out.close();
}
}
catch (IOException ioe)
{
// best efforts to close, exit silently
}
}
}
}