JavaNIO - Scatter & Gather

Scatter & Gather指在多个缓冲区上实现一个简单的 I/O 操作。减少或避免了Buffer间的拷贝和系统调用。

Channel Write操作

Write操作

Channel Read操作

Read操作

public class ChannelDemo {
    public static void main(String[] args) throws IOException {
        ByteBuffer buffer1 = ByteBuffer.allocate(4);
        ByteBuffer buffer2 = ByteBuffer.allocate(6);
        ByteBuffer[] buffers = {buffer1, buffer2};

        System.out.println("===Channel Read 即Scatter===");
        FileInputStream fis = new FileInputStream("d:/temp/x.dat");
        ScatteringByteChannel scatteringByteChannel = (ScatteringByteChannel) Channels.newChannel(fis);

        scatteringByteChannel.read(buffers);//数据从Channel 散布到各个 buffers

        buffer1.flip();
        System.out.println(new String(buffer1.array()));
        System.out.println(new String(buffer2.array()));

        while (buffer1.hasRemaining()) {
            System.out.println(buffer1.get());
        }

        buffer2.flip();
        while (buffer2.hasRemaining()) {
            System.out.println(buffer2.get());
        }
        System.out.println("===Channel Write 即Gather===");
        buffer1.rewind();
        buffer2.rewind();

        FileOutputStream fos = new FileOutputStream("d:/temp/y.dat");
        GatheringByteChannel gatheringByteChannel = (GatheringByteChannel) Channels.newChannel(fos);
        buffers[0] = buffer2;
        buffers[1] = buffer1;
        gatheringByteChannel.write(buffers);//数据从各个 buffers 抽取到Channel
    }
}

Scatter& Gather优点

Scatter/Gather 操作会被翻译为适当的本地调用来直接填充或抽取缓冲区，减少或避免了缓冲区拷贝和系统调用

public final Buffer clear() {
       position = 0;
       limit = capacity;
       mark = -1;
       return this;
  }
  public final Buffer rewind() {
      position = 0;
      mark = -1;
      return this;
  }