iobuffer.java

mina是以Java实现的一个开源的网络程序框架

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 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
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 *    http://www.apache.org/licenses/LICENSE-2.0
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 *  KIND, either express or implied.  See the License for the
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package org.apache.mina.core.buffer;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.CharBuffer;
import java.nio.DoubleBuffer;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.nio.LongBuffer;
import java.nio.ReadOnlyBufferException;
import java.nio.ShortBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.util.EnumSet;
import java.util.Set;

import org.apache.mina.core.session.IoSession;

/**
 * A byte buffer used by MINA applications.
 * <p>
 * This is a replacement for {@link ByteBuffer}. Please refer to
 * {@link ByteBuffer} documentation for preliminary usage.  MINA does
 * not use NIO {@link ByteBuffer} directly for two reasons:
 * <ul>
 * <li>It doesn't provide useful getters and putters such as
 * <code>fill</code>, <code>get/putString</code>, and
 * <code>get/putAsciiInt()</code> enough.</li>
 * <li>It is difficult to write variable-length data due to its fixed
 * capacity</li>
 * </ul>
 * </p>
 *
 * <h2>Allocation</h2>
 * <p>
 * You can allocate a new heap buffer.
 * <pre>
 * IoBuffer buf = IoBuffer.allocate(1024, false);
 * </pre>
 * you can also allocate a new direct buffer:
 * <pre>
 * IoBuffer buf = IoBuffer.allocate(1024, true);
 * </pre>
 * or you can set the default buffer type.
 * <pre>
 * // Allocate heap buffer by default.
 * IoBuffer.setUseDirectBuffer(false);
 * // A new heap buffer is returned.
 * IoBuffer buf = IoBuffer.allocate(1024);
 * </pre>
 * </p>
 *
 * <h2>Wrapping existing NIO buffers and arrays</h2>
 * <p>
 * This class provides a few <tt>wrap(...)</tt> methods that wraps
 * any NIO buffers and byte arrays.
 *
 * <h2>AutoExpand</h2>
 * <p>
 * Writing variable-length data using NIO <tt>ByteBuffers</tt> is not really
 * easy, and it is because its size is fixed.  {@link IoBuffer} introduces 
 * <tt>autoExpand</tt> property.  If <tt>autoExpand</tt> property is true, you
 * never get {@link BufferOverflowException} or
 * {@link IndexOutOfBoundsException} (except when index is negative).
 * It automatically expands its capacity and limit value.  For example:
 * <pre>
 * String greeting = messageBundle.getMessage( "hello" );
 * IoBuffer buf = IoBuffer.allocate( 16 );
 * // Turn on autoExpand (it is off by default)
 * buf.setAutoExpand( true );
 * buf.putString( greeting, utf8encoder );
 * </pre>
 * The underlying {@link ByteBuffer} is reallocated by {@link IoBuffer} behind
 * the scene if the encoded data is larger than 16 bytes in the example above.
 * Its capacity will double, and its limit will increase to the last position
 * the string is written.
 * </p>
 * 
 * <h2>AutoShrink</h2>
 * <p>
 * You might also want to decrease the capacity of the buffer when most
 * of the allocated memory area is not being used.  {@link IoBuffer} provides
 * <tt>autoShrink</tt> property to take care of this issue.  If 
 * <tt>autoShrink</tt> is turned on, {@link IoBuffer} halves the capacity
 * of the buffer when {@link #compact()} is invoked and only 1/4 or less of
 * the current capacity is being used.
 * <p>
 * You can also {@link #shrink()} method manually to shrink the capacity of
 * the buffer.
 * <p> 
 * The underlying {@link ByteBuffer} is reallocated by {@link IoBuffer} behind
 * the scene, and therefore {@link #buf()} will return a different
 * {@link ByteBuffer} instance once capacity changes.  Please also note
 * {@link #compact()} or {@link #shrink()} will not decrease the capacity if
 * the new capacity is less than the {@link #minimumCapacity()} of the buffer.
 *
 * <h2>Derived Buffers</h2>
 * <p>
 * Derived buffers are the buffers which were created by
 * {@link #duplicate()}, {@link #slice()}, or {@link #asReadOnlyBuffer()}.
 * They are useful especially when you broadcast the same messages to
 * multiple {@link IoSession}s.  Please note that the buffer derived from and
 * its derived buffers are not both auto-expandable neither auto-shrinkable.
 * Trying to call {@link #setAutoExpand(boolean)} or {@link #setAutoShrink(boolean)}
 * with <tt>true</tt> parameter will raise an {@link IllegalStateException}.
 * </p>
 *
 * <h2>Changing Buffer Allocation Policy</h2>
 * <p>
 * {@link IoBufferAllocator} interface lets you override the default buffer
 * management behavior.  There are two allocators provided out-of-the-box:
 * <ul>
 * <li>{@link SimpleBufferAllocator} (default)</li>
 * <li>{@link CachedBufferAllocator}</li>
 * </ul>
 * You can implement your own allocator and use it by calling
 * {@link #setAllocator(IoBufferAllocator)}.
 * </p>
 *
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev: 748525 $, $Date: 2009-02-27 14:45:31 +0100 (Fri, 27 Feb 2009) $
 */
public abstract class IoBuffer implements Comparable<IoBuffer> {
    /** The allocator used to create new buffers */
    private static IoBufferAllocator allocator = new SimpleBufferAllocator();

    /** A flag indicating which type of buffer we are using : heap or direct */
    private static boolean useDirectBuffer = false;

    /**
     * Returns the allocator used by existing and new buffers
     */
    public static IoBufferAllocator getAllocator() {
        return allocator;
    }

    /**
     * Sets the allocator used by existing and new buffers
     */
    public static void setAllocator(IoBufferAllocator newAllocator) {
        if (newAllocator == null) {
            throw new NullPointerException("allocator");
        }

        IoBufferAllocator oldAllocator = allocator;

        allocator = newAllocator;

        if (null != oldAllocator) {
            oldAllocator.dispose();
        }
    }

    /**
     * Returns <tt>true</tt> if and only if a direct buffer is allocated
     * by default when the type of the new buffer is not specified.  The
     * default value is <tt>false</tt>.
     */
    public static boolean isUseDirectBuffer() {
        return useDirectBuffer;
    }

    /**
     * Sets if a direct buffer should be allocated by default when the
     * type of the new buffer is not specified.  The default value is
     * <tt>false</tt>.
     */
    public static void setUseDirectBuffer(boolean useDirectBuffer) {
        IoBuffer.useDirectBuffer = useDirectBuffer;
    }

    /**
     * Returns the direct or heap buffer which is capable to store the
     * specified amount of bytes.
     *
     * @param capacity the capacity of the buffer
     *
     * @see #setUseDirectBuffer(boolean)
     */
    public static IoBuffer allocate(int capacity) {
        return allocate(capacity, useDirectBuffer);
    }

    /**
     * Returns the buffer which is capable of the specified size.
     *
     * @param capacity the capacity of the buffer
     * @param direct   <tt>true</tt> to get a direct buffer,
     *                 <tt>false</tt> to get a heap buffer.
     */
    public static IoBuffer allocate(int capacity, boolean direct) {
        if (capacity < 0) {
            throw new IllegalArgumentException("capacity: " + capacity);
        }

        return allocator.allocate(capacity, direct);
    }

    /**
     * Wraps the specified NIO {@link ByteBuffer} into MINA buffer.
     */
    public static IoBuffer wrap(ByteBuffer nioBuffer) {
        return allocator.wrap(nioBuffer);
    }

    /**
     * Wraps the specified byte array into MINA heap buffer.
     */
    public static IoBuffer wrap(byte[] byteArray) {
        return wrap(ByteBuffer.wrap(byteArray));
    }

    /**
     * Wraps the specified byte array into MINA heap buffer.
     */
    public static IoBuffer wrap(byte[] byteArray, int offset, int length) {
        return wrap(ByteBuffer.wrap(byteArray, offset, length));
    }

    /**
     * Normalizes the specified capacity of the buffer to power of 2,
     * which is often helpful for optimal memory usage and performance. 
     * If it is greater than or equal to {@link Integer#MAX_VALUE}, it
     * returns {@link Integer#MAX_VALUE}.  If it is zero, it returns zero.
     */
    protected static int normalizeCapacity(int requestedCapacity) {
        switch (requestedCapacity) {
        case 0:
        case 1 << 0:
        case 1 << 1:
        case 1 << 2:
        case 1 << 3:
        case 1 << 4:
        case 1 << 5:
        case 1 << 6:
        case 1 << 7:
        case 1 << 8:
        case 1 << 9:
        case 1 << 10:
        case 1 << 11:
        case 1 << 12:
        case 1 << 13:
        case 1 << 14:
        case 1 << 15:
        case 1 << 16:
        case 1 << 17:
        case 1 << 18:
        case 1 << 19:
        case 1 << 21:
        case 1 << 22:
        case 1 << 23:
        case 1 << 24:
        case 1 << 25:
        case 1 << 26:
        case 1 << 27:
        case 1 << 28:
        case 1 << 29:
        case 1 << 30:
        case Integer.MAX_VALUE:
            return requestedCapacity;
        }

        int newCapacity = 1;
        while (newCapacity < requestedCapacity) {
            newCapacity <<= 1;
            if (newCapacity < 0) {
                return Integer.MAX_VALUE;
            }
        }
        return newCapacity;
    }
    
    /**
     * Creates a new instance.  This is an empty constructor.
     */
    protected IoBuffer() {
    }

    /**
     * Declares this buffer and all its derived buffers are not used anymore
     * so that it can be reused by some {@link IoBufferAllocator} implementations.
     * It is not mandatory to call this method, but you might want to invoke this
     * method for maximum performance. 
     */
    public abstract void free();

    /**
     * Returns the underlying NIO buffer instance.
     */
    public abstract ByteBuffer buf();

    /**
     * @see ByteBuffer#isDirect()
     */
    public abstract boolean isDirect();

    /**
     * returns <tt>true</tt> if and only if this buffer is derived from other buffer
     * via {@link #duplicate()}, {@link #slice()} or {@link #asReadOnlyBuffer()}.
     */
    public abstract boolean isDerived();

    /**
     * @see ByteBuffer#isReadOnly()
     */
    public abstract boolean isReadOnly();

    /**
     * Returns the minimum capacity of this buffer which is used to determine
     * the new capacity of the buffer shrunk by {@link #compact()} and
     * {@link #shrink()} operation.  The default value is the initial capacity
     * of the buffer.
     */
    public abstract int minimumCapacity();

    /**
     * Sets the minimum capacity of this buffer which is used to determine
     * the new capacity of the buffer shrunk by {@link #compact()} and
     * {@link #shrink()} operation.  The default value is the initial capacity
     * of the buffer.
     */
    public abstract IoBuffer minimumCapacity(int minimumCapacity);

    /**
     * @see ByteBuffer#capacity()
     */
    public abstract int capacity();

    /**
     * Increases the capacity of this buffer.  If the new capacity is less than
     * or equal to the current capacity, this method returns silently.  If the
     * new capacity is greater than the current capacity, the buffer is
     * reallocated while retaining the position, limit, mark and the content
     * of the buffer.
     */
    public abstract IoBuffer capacity(int newCapacity);

    /**
     * Returns <tt>true</tt> if and only if <tt>autoExpand</tt> is turned on.
     */
    public abstract boolean isAutoExpand();

    /**
     * Turns on or off <tt>autoExpand</tt>.
     */
    public abstract IoBuffer setAutoExpand(boolean autoExpand);

    /**
     * Returns <tt>true</tt> if and only if <tt>autoShrink</tt> is turned on.
     */
    public abstract boolean isAutoShrink();

    /**
     * Turns on or off <tt>autoShrink</tt>.
     */
    public abstract IoBuffer setAutoShrink(boolean autoShrink);

    /**
     * Changes the capacity and limit of this buffer so this buffer get
     * the specified <tt>expectedRemaining</tt> room from the current position.
     * This method works even if you didn't set <tt>autoExpand</tt> to
     * <tt>true</tt>.
     */
    public abstract IoBuffer expand(int expectedRemaining);

    /**
     * Changes the capacity and limit of this buffer so this buffer get
     * the specified <tt>expectedRemaining</tt> room from the specified
     * <tt>position</tt>.
     * This method works even if you didn't set <tt>autoExpand</tt> to
     * <tt>true</tt>.
     */
    public abstract IoBuffer expand(int position, int expectedRemaining);

    /**
     * Changes the capacity of this buffer so this buffer occupies as less
     * memory as possible while retaining the position, limit and the
     * buffer content between the position and limit.  The capacity of the
     * buffer never becomes less than {@link #minimumCapacity()}.
     * The mark is discarded once the capacity changes.
     */
    public abstract IoBuffer shrink();

    /**
     * @see java.nio.Buffer#position()
     */
    public abstract int position();

    /**
     * @see java.nio.Buffer#position(int)
     */
    public abstract IoBuffer position(int newPosition);

    /**
     * @see java.nio.Buffer#limit()
     */
    public abstract int limit();

    /**
     * @see java.nio.Buffer#limit(int)
     */
    public abstract IoBuffer limit(int newLimit);

    /**
     * @see java.nio.Buffer#mark()
     */
    public abstract IoBuffer mark();

    /**
     * Returns the position of the current mark.  This method returns <tt>-1</tt> if no
     * mark is set.
     */
    public abstract int markValue();

    /**
     * @see java.nio.Buffer#reset()
     */
    public abstract IoBuffer reset();

    /**
     * @see java.nio.Buffer#clear()
     */
    public abstract IoBuffer clear();

    /**
     * Clears this buffer and fills its content with <tt>NUL</tt>.
     * The position is set to zero, the limit is set to the capacity,
     * and the mark is discarded.
     */
    public abstract IoBuffer sweep();

    /**double
     * Clears this buffer and fills its content with <tt>value</tt>.
     * The position is set to zero, the limit is set to the capacity,
     * and the mark is discarded.
     */
    public abstract IoBuffer sweep(byte value);