1,代码实例

  FileInputStream inputStream=new FileInputStream("input.txt");
        FileOutputStream outputStream  =new FileOutputStream("output.txt");

        FileChannel channel1 = inputStream.getChannel();
        FileChannel channel2 = outputStream.getChannel();

        ByteBuffer buffer= ByteBuffer.allocate(512);

        while(true)
        {
            buffer.clear();
            int read=channel1.read(buffer);
            System.out.println("read: "+read);
            if(-1==read)
            {
              break;
            }
            buffer.flip();
            channel2.write(buffer);
        }
        channel1.close();
        channel2.close();

将input.txt的内容读取到output.txt

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2,buffer的详解

2.1 allocate

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2.2 slice方法

/**
     * Creates a new byte buffer whose content is a shared subsequence of
     * this buffer's content.
     * 创造一个新的字节buffer和当前buffer共享buffer的content
     * <p> The content of the new buffer will start at this buffer's current
     * position.  Changes to this buffer's content will be visible in the new
     * buffer, and vice versa; the two buffers' position, limit, and mark
     * values will be independent.
     *
     * <p> The new buffer's position will be zero, its capacity and its limit
     * will be the number of bytes remaining in this buffer, and its mark
     * will be undefined.  The new buffer will be direct if, and only if, this
     * buffer is direct, and it will be read-only if, and only if, this buffer
     * is read-only.  </p>
     *
     * @return  The new byte buffer
     */
    public abstract ByteBuffer slice();

  ByteBuffer buffer= ByteBuffer.allocate(10);
        for(int i=0;i<buffer.capacity();i++)
        {
            buffer.put((byte)i);
        }
        buffer.position(2);
        buffer.limit(6);
        ByteBuffer sliceBuffer=buffer.slice();
        for(int i = 0; i < sliceBuffer.capacity(); ++i) {
            byte b = sliceBuffer.get(i);
            b *= 2;
            sliceBuffer.put(i, b);
        }
        buffer.position(0);
        buffer.limit(buffer.capacity());

        while(buffer.hasRemaining()) {
            System.out.println(buffer.get());
        }

将2到6的内容大写

2.3 只读buffer

 /**
     * Creates a new, read-only byte buffer that shares this buffer's
     * content.
     *创造一个新的只读buffer和当前的buffer共享内容
     * <p> The content of the new buffer will be that of this buffer.  Changes
     * to this buffer's content will be visible in the new buffer; the new
     * buffer itself, however, will be read-only and will not allow the shared
     * content to be modified.  The two buffers' position, limit, and mark
     * values will be independent.
     * 不能修改,但是两个buffer的三个属性都是独立的
     * <p> The new buffer's capacity, limit, position, and mark values will be
     * identical to those of this buffer.
     *
     * <p> If this buffer is itself read-only then this method behaves in
     * exactly the same way as the {@link #duplicate duplicate} method.  </p>
     *
     * @return  The new, read-only byte buffer
     */
    public abstract ByteBuffer asReadOnlyBuffer();

2.4 allocateDirect

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在buffer中

public abstract class Buffer {

    /**
     * The characteristics of Spliterators that traverse and split elements
     * maintained in Buffers.
     */
    static final int SPLITERATOR_CHARACTERISTICS =
        Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.ORDERED;

    // Invariants: mark <= position <= limit <= capacity
    private int mark = -1;
    private int position = 0;
    private int limit;
    private int capacity;

    // Used only by direct buffers
   为直接内容使用
    // NOTE: hoisted here for speed in JNI GetDirectBufferAddress
    写在这儿视为了提高获取的速率
    long address;