circularobjectbuffer.java

java操作excel的类

/*
 * Circular Object Buffer
 * Copyright (C) 2002 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.
 */
package com.Ostermiller.util;

/**
 * Implements the Circular Buffer producer/consumer model for Objects.
 * More information about this class is available from <a target="_top" href=
 * "http://ostermiller.org/utils/CircularObjectBuffer.html">ostermiller.org</a>.
 * <p>
 * This class is thread safe.
 *
 * @see CircularCharBuffer
 * @see CircularByteBuffer
 *
 * @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
 * @since ostermillerutils 1.00.00
 */
public class CircularObjectBuffer {

	/**
	 * The default size for a circular object buffer.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	private final static int DEFAULT_SIZE = 1024;

	/**
	 * A buffer that will grow as things are added.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public final static int INFINITE_SIZE = -1;

	/**
	 * The circular buffer.
	 * <p>
	 * The actual capacity of the buffer is one less than the actual length
	 * of the buffer so that an empty and a full buffer can be
	 * distinguished.  An empty buffer will have the readPostion and the
	 * writePosition equal to each other.  A full buffer will have
	 * the writePosition one less than the readPostion.
	 * <p>
	 * There are two important indexes into the buffer:
	 * The readPosition, and the writePosition. The Objects
	 * available to be read go from the readPosition to the writePosition,
	 * wrapping around the end of the buffer.  The space available for writing
	 * goes from the write position to one less than the readPosition,
	 * wrapping around the end of the buffer.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected Object[] buffer;
	/**
	 * Index of the first Object available to be read.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int readPosition = 0;
	/**
	 * Index of the first Object available to be written.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile int writePosition = 0;
	/**
	 * If this buffer is infinite (should resize itself when full)
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected volatile boolean infinite = false;
	/**
	 * True if a write to a full buffer should block until the buffer
	 * has room, false if the write method should throw an IOException
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected boolean blockingWrite = true;

	/**
	 * True when no more input is coming into this buffer.  At that
	 * point reading from the buffer may return  null if the buffer
	 * is empty, otherwise a read will block until an Object is available.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	protected boolean inputDone = false;

	/**
	 * Make this buffer ready for reuse.  The contents of the buffer
	 * will be cleared and the streams associated with this buffer
	 * will be reopened if they had been closed.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public void clear(){
		synchronized (this){
			readPosition = 0;
			writePosition = 0;
			inputDone = false;
		}
	}

	/**
	 * Get number of Objects that are available to be read.
	 * <p>
	 * Note that the number of Objects available plus
	 * the number of Objects free may not add up to the
	 * capacity of this buffer, as the buffer may reserve some
	 * space for other purposes.
	 *
	 * @return the size in Objects of this buffer
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public int getAvailable(){
		synchronized (this){
			return available();
		}
	}

	/**
	 * Get the number of Objects this buffer has free for
	 * writing.
	 * <p>
	 * Note that the number of Objects available plus
	 * the number of Objects free may not add up to the
	 * capacity of this buffer, as the buffer may reserve some
	 * space for other purposes.
	 *
	 * @return the available space in Objects of this buffer
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public int getSpaceLeft(){
		synchronized (this){
			return spaceLeft();
		}
	}

	/**
	 * Get the capacity of this buffer.
	 * <p>
	 * Note that the number of Objects available plus
	 * the number of Objects free may not add up to the
	 * capacity of this buffer, as the buffer may reserve some
	 * space for other purposes.
	 *
	 * @return the size in Objects of this buffer
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public int getSize(){
		synchronized (this){
			return buffer.length;
		}
	}

	/**
	 * double the size of the buffer
	 *
	 * @since ostermillerutils 1.00.00
	 */
	private void resize(){
		Object[] newBuffer = new Object[buffer.length * 2];
		int available = available();
		if (readPosition <= writePosition){
			// any space between the read and
			// the first write needs to be saved.
			// In this case it is all in one piece.
			int length = writePosition - readPosition;
			System.arraycopy(buffer, readPosition, newBuffer, 0, length);
		} else {
			int length1 = buffer.length - readPosition;
			System.arraycopy(buffer, readPosition, newBuffer, 0, length1);
			int length2 = writePosition;
			System.arraycopy(buffer, 0, newBuffer, length1, length2);
		}
		buffer = newBuffer;
		readPosition = 0;
		writePosition = available;
	}

	/**
	 * Space available in the buffer which can be written.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	private int spaceLeft(){
		if (writePosition < readPosition){
			// any space between the first write and
			// the read except one Object is available.
			// In this case it is all in one piece.
			return (readPosition - writePosition - 1);
		} else {
			// space at the beginning and end.
			return ((buffer.length - 1) - (writePosition - readPosition));
		}
	}

	/**
	 * Objects available for reading.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	private int available(){
		if (readPosition <= writePosition){
			// any space between the first read and
			// the first write is available.  In this case i
			// is all in one piece.
			return (writePosition - readPosition);
		} else {
			// space at the beginning and end.
			return (buffer.length - (readPosition - writePosition));
		}
	}

	/**
	 * Create a new buffer with a default capacity.
	 * Writing to a full buffer will block until space
	 * is available rather than throw an exception.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public CircularObjectBuffer(){
		this (DEFAULT_SIZE, true);
	}

	/**
	 * Create a new buffer with given capacity.
	 * Writing to a full buffer will block until space
	 * is available rather than throw an exception.
	 * <p>
	 * Note that the buffer may reserve some Objects for
	 * special purposes and capacity number of Objects may
	 * not be able to be written to the buffer.
	 * <p>
	 * Note that if the buffer is of INFINITE_SIZE it will
	 * neither block or throw exceptions, but rather grow
	 * without bound.
	 *
	 * @param size desired capacity of the buffer in Objects or CircularObjectBuffer.INFINITE_SIZE.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public CircularObjectBuffer(int size){
		this (size, true);
	}

	/**
	 * Create a new buffer with a default capacity and
	 * given blocking behavior.
	 *
	 * @param blockingWrite true writing to a full buffer should block
	 *        until space is available, false if an exception should
	 *        be thrown instead.
	 *
	 * @since ostermillerutils 1.00.00
	 */
	public CircularObjectBuffer(boolean blockingWrite){
		this (DEFAULT_SIZE, blockingWrite);
	}

	/**
	 * Create a new buffer with the given capacity and
	 * blocking behavior.
	 * <p>
	 * Note that the buffer may reserve some Objects for
	 * special purposes and capacity number of Objects may