NIO - Scatter/Gather

转自：http://blog.csdn.net/java2000_wl/article/details/7619395

 

1.Scatter  从一个Channel读取的信息分散到N个缓冲区中(Buufer).

2.Gather  将N个Buffer里面内容按照顺序发送到一个Channel.  

    Scatter/Gather功能是通道(Channel)提供的  并不是Buffer,

Scatter/Gather相关接口 类图

    ReadableByteChannel WritableByteChannel     接口提供了通道的读写功能

    ScatteringByteChannel  GatheringByteChannel接口都新增了两个以缓冲区数组作为参数的相应方法

   以FileChannel为例

   *Scatter

       /**
 * Scatter
 * <br>------------------------------<br>
 * @param fileName
 * @throws IOException
 * @see FileChannel.read(java.nio.ByteBuffer[])
 */
private static void scatter(final String fileName) throws IOException {
    RandomAccessFile accessFile = new RandomAccessFile(fileName, "r");
    //获取文件通道
    FileChannel channel = accessFile.getChannel();
    //创建两个缓冲区
    ByteBuffer headBuffer = ByteBuffer.allocate(2);
    ByteBuffer bodyBuffer = ByteBuffer.allocate(1024);

    ByteBuffer[] allBuffers = new ByteBuffer[]{headBuffer, bodyBuffer};
    // headBuffer 前10个字节
    // bodyBuffer 剩下的
    long n = channel.read(allBuffers);
    System.out.println("共读到多少字节:" + n);

    headBuffer.flip();
    //head缓冲区中的数据:qw
    System.out.println("head缓冲区中的数据:" + charset.decode(headBuffer));

    bodyBuffer.flip();
    //body缓冲区中的数据:ertyuiop
    System.out.println("body缓冲区中的数据:" + charset.decode(bodyBuffer));
    accessFile.close();
    channel.close();
}

/**
 * Scatter2
 * <br>------------------------------<br>
 * @param fileName
 * @throws IOException
 * @see FileChannel.read(java.nio.ByteBuffer[], int, int)
 */
private static void scatter2(final String fileName) throws IOException {
    RandomAccessFile accessFile = new RandomAccessFile(fileName, "r");
    //获取文件通道
    FileChannel channel = accessFile.getChannel();
    //创建五个缓冲区
    ByteBuffer headBuffer = ByteBuffer.allocate(2);
    ByteBuffer bodyBuffer1 = ByteBuffer.allocate(3);
    ByteBuffer bodyBuffer2 = ByteBuffer.allocate(2);
    ByteBuffer bodyBuffer3 = ByteBuffer.allocate(2);
    ByteBuffer bodyBuffer4 = ByteBuffer.allocate(1);

    ByteBuffer[] allBuffers = new ByteBuffer[]{
            headBuffer,
            bodyBuffer1, bodyBuffer2,
            bodyBuffer3, bodyBuffer4,};
    //0从那个缓冲区开始被使用    使用3个缓冲区
    //会使用 headBuffer,bodyBuffer1,bodyBuffer2
    long n = channel.read(allBuffers, 0, 3);

    System.out.println("共读到多少字节:" + n);

    headBuffer.flip();
    //head缓冲区中的数据:qw
    System.out.println("head缓冲区中的数据:" + charset.decode(headBuffer));

    bodyBuffer1.flip();
    //body1缓冲区中的数据:ert
    System.out.println("body1缓冲区中的数据:" + charset.decode(bodyBuffer1));

    bodyBuffer2.flip();
    //body2缓冲区中的数据:yu
    System.out.println("body2缓冲区中的数据:" + charset.decode(bodyBuffer2));

    bodyBuffer3.flip();
    //body3，没有数据
    System.out.println("body3缓冲区中的数据:" + charset.decode(bodyBuffer3));

    bodyBuffer4.flip();
    //body4没有数据
    System.out.println("body4缓冲区中的数据:" + charset.decode(bodyBuffer4));

    accessFile.close();
    channel.close();
}

/**
 *
 * <br>------------------------------<br>
 * @param fileName
 * @throws IOException
 */
private static void writeData(final String fileName, String data) throws IOException {
    RandomAccessFile accessFile = new RandomAccessFile(fileName, "rw");
    accessFile.writeBytes(data);
    accessFile.close();
}

private static Charset charset = Charset.forName("GBK");

public static void main(String[] args) throws IOException {
    final String fileName = "D:/test.log";
    //先写入10个字节数据 以便测试 scatter模式
    writeData(fileName, "qwertyuiop");

    /**----------Scatter------------*/
    //read(java.nio.ByteBuffer[])
    scatter(fileName);

    //read(java.nio.ByteBuffer[], int, int)
    scatter2(fileName);
}

*Gather

/**
 * gather
 * <br>------------------------------<br>
 * @param fileName
 * @throws IOException
 * @see FileChannel#write(java.nio.ByteBuffer[])
 */
private static void gather(String fileName) throws IOException {
    RandomAccessFile accessFile = new RandomAccessFile(fileName, "rw");
    //获取文件通道
    FileChannel channel = accessFile.getChannel();
    //创建两个缓冲区
    ByteBuffer headBuffer = ByteBuffer.allocate(3);
    headBuffer.put("abc".getBytes());

    ByteBuffer bodyBuffer = ByteBuffer.allocate(1024);
    bodyBuffer.put("defg".getBytes());

    ByteBuffer[] allBuffers = new ByteBuffer[]{headBuffer, bodyBuffer};

    headBuffer.flip();
    bodyBuffer.flip();

    //将按allBuffers顺序  写入abcdefg
    long n = channel.write(allBuffers);

    System.out.println("共写入多少字节:" + n);

    accessFile.close();
    channel.close();
}

/**
 * gather2
 * <br>------------------------------<br>
 * @param fileName
 * @throws IOException
 * @see FileChannel#write(java.nio.ByteBuffer[], int, int)
 */
private static void gather2(String fileName) throws IOException {
    RandomAccessFile accessFile = new RandomAccessFile(fileName, "rw");
    //获取文件通道
    FileChannel channel = accessFile.getChannel();
    //创建两个缓冲区
    ByteBuffer headBuffer = ByteBuffer.allocate(3);
    ByteBuffer bodyBuffer1 = ByteBuffer.allocate(4);
    ByteBuffer bodyBuffer2 = ByteBuffer.allocate(20);
    ByteBuffer bodyBuffer3 = ByteBuffer.allocate(20);
    ByteBuffer bodyBuffer4 = ByteBuffer.allocate(20);

    headBuffer.put("abc".getBytes());
    bodyBuffer1.put("defg".getBytes());
    bodyBuffer2.put("bnbnbnb".getBytes());
    bodyBuffer3.put("zzz444".getBytes());

    ByteBuffer[] allBuffers = new ByteBuffer[]{
            headBuffer,
            bodyBuffer1, bodyBuffer2,
            bodyBuffer3, bodyBuffer4,};

    headBuffer.flip();
    bodyBuffer1.flip();
    bodyBuffer2.flip();
    bodyBuffer3.flip();
    bodyBuffer4.flip();

    //将按allBuffers数组顺序使用两个缓冲区
    //0从哪开始
    //2使用几个
    //当前使用headBuffer  bodyBuffer1
    //最终写入abcdefg
    long n = channel.write(allBuffers, 0, 2);

    //应该返回7个字节
    System.out.println("共写入多少字节:" + n);

    accessFile.close();
    channel.close();
}

private static Charset charset = Charset.forName("GBK");

public static void main(String[] args) throws IOException {
    final String fileName = "D:/test.log";
    /**----------Gather------------*/
    //FileChannel#write(java.nio.ByteBuffer[])
    gather(fileName);

    //FileChannel#write(java.nio.ByteBuffer[], int, int)
    gather2(fileName);
}