Reads sequentially from multiple sources
/*
* Copyright (C) 2004 Stephen Ostermiller
* http://ostermiller.org/contact.pl?regarding=Java+Utilities
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* See COPYING.TXT for details.
*/
import java.io.*;
import java.util.ArrayList;
/**
* A reader which reads sequentially from multiple sources.
* More information about this class is available from <a target="_top" href=
* "http://ostermiller.org/utils/">ostermiller.org</a>.
*
* @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
* @since ostermillerutils 1.04.00
*/
public class ConcatReader extends Reader {
/**
* Current index to readerQueue
*
* @since ostermillerutils 1.04.01
*/
private int readerQueueIndex = 0;
/**
* Queue of readers that have yet to be read from.
*
* @since ostermillerutils 1.04.01
*/
private ArrayList<Reader> readerQueue = new ArrayList<Reader>();
/**
* A cache of the current reader from the readerQueue
* to avoid unneeded access to the queue which must
* be synchronized.
*
* @since ostermillerutils 1.04.01
*/
private Reader currentReader = null;
/**
* true iff the client may add more readers.
*
* @since ostermillerutils 1.04.01
*/
private boolean doneAddingReaders = false;
/**
* Causes the addReader method to throw IllegalStateException
* and read() methods to return -1 (end of stream)
* when there is no more available data.
* <p>
* Calling this method when this class is no longer accepting
* more readers has no effect.
*
* @since ostermillerutils 1.04.01
*/
public void lastReaderAdded(){
doneAddingReaders = true;
}
/**
* Add the given reader to the queue of readers from which to
* concatenate data.
*
* @param in Reader to add to the concatenation.
* @throws IllegalStateException if more readers can't be added because lastReaderAdded() has been called, close() has been called, or a constructor with reader parameters was used.
*
* @since ostermillerutils 1.04.01
*/
public void addReader(Reader in){
synchronized(readerQueue){
if (in == null) throw new NullPointerException();
if (closed) throw new IllegalStateException("ConcatReader has been closed");
if (doneAddingReaders) throw new IllegalStateException("Cannot add more readers - the last reader has already been added.");
readerQueue.add(in);
}
}
/**
* Add the given reader to the queue of readers from which to
* concatenate data.
*
* @param in Reader to add to the concatenation.
* @throws IllegalStateException if more readers can't be added because lastReaderAdded() has been called, close() has been called, or a constructor with reader parameters was used.
* @throws NullPointerException the array of readers, or any of the contents is null.
*
* @since ostermillerutils 1.04.01
*/
public void addReaders(Reader[] in){
for (Reader element: in) {
addReader(element);
}
}
/**
* Gets the current reader, looking at the next
* one in the list if the current one is null.
*
* @since ostermillerutils 1.04.01
*/
private Reader getCurrentReader(){
if (currentReader == null && readerQueueIndex < readerQueue.size()){
synchronized(readerQueue){
// reader queue index is advanced only by the nextReader()
// method. Don't do it here.
currentReader = readerQueue.get(readerQueueIndex);
}
}
return currentReader;
}
/**
* Indicate that we are done with the current reader and we should
* advance to the next reader.
*
* @since ostermillerutils 1.04.01
*/
private void advanceToNextReader(){
currentReader = null;
readerQueueIndex++;
}
/**
* True iff this the close() method has been called on this stream.
*
* @since ostermillerutils 1.04.00
*/
private boolean closed = false;
/**
* Create a new reader that can dynamically accept new sources.
* <p>
* New sources should be added using the addReader() method.
* When all sources have been added the lastReaderAdded() should
* be called so that read methods can return -1 (end of stream).
* <p>
* Adding new sources may by interleaved with read calls.
*
* @since ostermillerutils 1.04.01
*/
public ConcatReader(){
// Empty Constructor
}
/**
* Create a new reader with one source.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in reader to use as a source.
*
* @throws NullPointerException if in is null
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader in){
addReader(in);
lastReaderAdded();
}
/**
* Create a new reader with two sources.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in1 first reader to use as a source.
* @param in2 second reader to use as a source.
*
* @throws NullPointerException if either source is null.
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader in1, Reader in2){
addReader(in1);
addReader(in2);
lastReaderAdded();
}
/**
* Create a new reader with an arbitrary number of sources.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in readers to use as a sources.
*
* @throws NullPointerException if the input array on any element is null.
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader[] in){
addReaders(in);
lastReaderAdded();
}
/**
* Read a single character. This method will block until a
* character is available, an I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @return The character read, as an integer in the range 0 to 65535 (0x00-0xffff),
* or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public int read() throws IOException {
if (closed) throw new IOException("Reader closed");
int r = -1;
while (r == -1){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return -1;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
r = in.read();
if (r == -1) advanceToNextReader();
}
}
return r;
}
/**
* Read characters into an array. This method will block until some input is available, an
* I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param cbuf - Destination buffer
* @return The number of characters read, or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
* @throws NullPointerException - If the buffer is null.
*
* @since ostermillerutils 1.04.00
*/
@Override public int read(char[] cbuf) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Read characters into a portion of an array. This method will block until
* some input is available, an I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param cbuf Destination buffer
* @param off Offset at which to start storing characters
* @param len Maximum number of characters to read
* @return The number of characters read, or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
* @throws NullPointerException - If the buffer is null.
* @throws IndexOutOfBoundsException - if length or offset are not possible.
*
* @since ostermillerutils 1.04.00
*/
@Override public int read(char[] cbuf, int off, int len) throws IOException {
if (off < 0 || len < 0 || off + len > cbuf.length) throw new IndexOutOfBoundsException();
if (closed) throw new IOException("Reader closed");
int r = -1;
while (r == -1){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return -1;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
r = in.read(cbuf, off, len);
if (r == -1) advanceToNextReader();
}
}
return r;
}
/**
* Skip characters. This method will block until some characters are
* available, an I/O error occurs, or the end of the stream is reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param n the number of characters to skip
* @return The number of characters actually skipped
*
* @throws IllegalArgumentException If n is negative.
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public long skip(long n) throws IOException {
if (closed) throw new IOException("Reader closed");
if (n <= 0) return 0;
long s = -1;
while (s <= 0){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return 0;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
s = in.skip(n);
// When nothing was skipped it is a bit of a puzzle.
// The most common cause is that the end of the underlying
// stream was reached. In which case calling skip on it
// will always return zero. If somebody were calling skip
// until it skipped everything they needed, there would
// be an infinite loop if we were to return zero here.
// If we get zero, let us try to read one character so
// we can see if we are at the end of the stream. If so,
// we will move to the next.
if (s <= 0) {
// read() will advance to the next stream for us, so don't do it again
s = ((read()==-1)?-1:1);
}
}
}
return s;
}
/**
* Tell whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input,
* false otherwise. Note that returning false does not guarantee that the next
* read will block.
*
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public boolean ready() throws IOException {
if (closed) throw new IOException("Reader closed");
Reader in = getCurrentReader();
if (in == null) return false;
return in.ready();
}
/**
* Close the stream and any underlying streams.
* Once a stream has been closed, further read(), ready(), mark(), or reset()
* invocations will throw an IOException. Closing a previously-closed stream,
* however, has no effect.
*
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public void close() throws IOException {
if (closed) return;
for (Reader reader: readerQueue) {
reader.close();
}
closed = true;
}
/**
* Mark not supported.
*
* @throws IOException because mark is not supported.
*
* @since ostermillerutils 1.04.00
*/
@Override public void mark(int readlimit) throws IOException {
throw new IOException("Mark not supported");
}
/**
* Reset not supported.
*
* @throws IOException because reset is not supported.
*
* @since ostermillerutils 1.04.00
*/
@Override public void reset() throws IOException {
throw new IOException("Reset not supported");
}
/**
* Mark not supported.
*
* @return false
*
* @since ostermillerutils 1.04.00
*/
@Override public boolean markSupported(){
return false;
}
}
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