ConcatReader.java Source Code

  • Concat Documentation and Examples
  • ConcatReader Javadoc
    /*
     * Copyright (C) 2004-2010 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 LICENSE.txt for details.
     */
    package com.Ostermiller.util;
    
    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;
    	}
    }