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/*
* $Id: XMLEventPipe.java,v 1.2 2004/07/05 23:46:51 cniles Exp $
*
* Copyright (c) 2004, Christian Niles, Unit12
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Christian Niles, Unit12, nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
*/
package javanet.staxutils;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLEventWriter;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.XMLEvent;
/**
* Provides the ability to pipe the {@link XMLEvent}s written to one
* {@link XMLEventWriter} to be read from a {@link XMLEventReader}. The
* implementation is based on a bounded-buffer with a specifiable maximum
* capacity. When that capacity is reached, the write end of the pipe will
* block until events are read from the read end. Similarly, when an attempt is
* made to read from an empty queue, the operation will block until more events
* are written to the buffer. The write end of the pipe will repair namespaces
* and buffer attribute/namespace events as defined in the specification of
* the {@link XMLEventWriter} interface.
*
* Both the read and write ends of this pipe are fully synchronized to allow
* multiple threads to read or write events to the pipe. However, care must be
* taken that the order of events is consistent, and that the stream is properly
* closed when writing is complete. If the write end is never closed the read
* end may block indefinitely, waiting for further events. To help prevent
* this, the write end will automatically close when an END_DOCUMENT event is
* written.
*
* To properly obey the expected behaviour of {@link XMLEventReader} and
* {@link javax.xml.stream.XMLStreamWriter}, methods such as
* {@link XMLEventReader#peek()} and {@link XMLEventReader#hasNext()} may block.
* This is necessary to prevent {@link XMLEventReader#hasNext()} from returning
* true just before the write end is closed, or false
* just before additional events are added. If the read end is closed before the
* writer, then the write end will silently discard all elements written to it
* until it is closed.
*
* @author Christian Niles
* @version $Revision: 1.2 $
*/
public class XMLEventPipe {
/**
* Default maximum number of events that may be stored by this pipe until
* the write end blocks.
*/
public static final int QUEUE_CAPACITY = 16;
/** List of events ready to be read. */
private List eventQueue = new LinkedList();
/** The maximum capacity of the queue, after which the pipe should block. */
private int capacity = QUEUE_CAPACITY;
/** Whether the read end has been closed. */
private boolean readEndClosed;
/** Whether the write end has been closed. */
private boolean writeEndClosed;
/**
* The read end of the pipe. This will be null until
* {@link #getReadEnd()} is called for the first time.
*/
private PipedXMLEventReader readEnd = new PipedXMLEventReader(this);
/**
* The write end of the pipe. This will be null until
* {@link #getWriteEnd()} is called for the first time.
*/
private PipedXMLEventWriter writeEnd = new PipedXMLEventWriter(this);
/**
* Constructs a new XMLEventPipe with the default capacity.
*/
public XMLEventPipe() {
}
/**
* Constructs a new XMLEventPipe with the specified capacity.
*
* @param capacity The number of events to buffer until the pipe will block.
* A number less than or equal to 0 means the pipe will buffer an
* unbounded number of events.
*/
public XMLEventPipe(int capacity) {
this.capacity = capacity;
}
/**
* Returns the read end of the pipe, from which events written to the write
* end of the pipe will be available.
*
* @return The read end of the pipe.
*/
public synchronized XMLEventReader getReadEnd() {
if (readEnd == null) {
readEnd = new PipedXMLEventReader(this);
}
return readEnd;
}
/**
* Returns the write end of the pipe, whose events will be available from
* the read end of this pipe.
*
* @return The write end of the pipe.
*/
public synchronized XMLEventWriter getWriteEnd() {
if (writeEnd == null) {
writeEnd = new PipedXMLEventWriter(this);
}
return writeEnd;
}
/**
* {@link XMLEventWriter} implementation used to provide the write end of
* the pipe.
*
* @author christian
* @version $Revision: 1.2 $
*/
private static final class PipedXMLEventWriter extends BaseXMLEventWriter {
/** The pipe we're connected to. */
private XMLEventPipe pipe;
public PipedXMLEventWriter(XMLEventPipe pipe) {
this.pipe = pipe;
}
public synchronized void close() throws XMLStreamException {
super.close();
synchronized (pipe) {
if (pipe.readEndClosed) {
pipe.eventQueue.clear();
}
pipe.writeEndClosed = true;
pipe.notifyAll();
}
}
protected void sendEvent(XMLEvent event) throws XMLStreamException {
synchronized (pipe) {
if (pipe.readEndClosed) {
// if read end is closed, throw away event
return;
}
if (pipe.capacity > 0) {
while (pipe.eventQueue.size() >= pipe.capacity) {
try {
pipe.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
pipe.eventQueue.add(event);
if (pipe.eventQueue.size() == 1) {
pipe.notifyAll();
}
if (event.isEndDocument()) {
close();
}
}
}
}
/**
* {@link XMLEventReader} implementation used to provide the read end of
* the pipe.
*
* @author christian
* @version $Revision: 1.2 $
*/
private static final class PipedXMLEventReader extends BaseXMLEventReader {
/** THe pipe this stream is connected to. */
private XMLEventPipe pipe;
public PipedXMLEventReader(XMLEventPipe pipe) {
this.pipe = pipe;
}
public synchronized XMLEvent nextEvent() throws XMLStreamException {
if (closed) {
throw new XMLStreamException("Stream has been closed");
}
synchronized (pipe) {
while (pipe.eventQueue.size() == 0) {
if (pipe.writeEndClosed) {
throw new NoSuchElementException("Stream has completed");
}
try {
pipe.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
boolean notify =
pipe.capacity > 0
&& pipe.eventQueue.size() >= pipe.capacity;
// remove next event from the queue
XMLEvent nextEvent = (XMLEvent) pipe.eventQueue.remove(0);
if (notify) {
pipe.notifyAll();
}
return nextEvent;
}
}
public synchronized boolean hasNext() {
if (closed) {
return false;
}
synchronized (pipe) {
while (pipe.eventQueue.size() == 0) {
if (pipe.writeEndClosed) {
break;
}
try {
pipe.wait();
} catch (InterruptedException e) {
}
}
return pipe.eventQueue.size() > 0;
}
}
public synchronized XMLEvent peek() throws XMLStreamException {
if (closed) {
return null;
}
synchronized (pipe) {
// wait until the queue has more events
while (pipe.eventQueue.size() == 0) {
if (pipe.writeEndClosed) {
return null;
}
try {
pipe.wait();
} catch (InterruptedException e) {
}
}
return (XMLEvent) pipe.eventQueue.get(0);
}
}
public synchronized void close() throws XMLStreamException {
if (closed) {
return;
}
synchronized (pipe) {
pipe.readEndClosed = true;
pipe.notifyAll();
}
super.close();
}
public void finalize() {
if (!closed) {
synchronized (pipe) {
pipe.readEndClosed = true;
pipe.notifyAll();
}
}
}
}
}
