JAVA NIO Scatter/Gather（矢量IO）

矢量IO=Scatter/Gather：

在多个缓冲区上实现一个简单的IO操作。减少或避免了缓冲区拷贝和系统调用（IO)

write：Gather

数据从几个缓冲区顺序抽取并沿着通道发送，就好比全部缓冲区全部连接起来放入一个大的缓冲区进行发送，缓冲区本身不具备gather能力。

read：Scatter

从通道读取的数据会按顺序散布到多个缓冲区，直到缓冲区被填满或者通道数据读完。

Gather：

Scatter：

示例代码：

/**
      * channel Gather/Scatter
      */
     public static void channelGatherScatter(){
         ByteBuffer head = ByteBuffer.allocate(4);
         ByteBuffer body = ByteBuffer.allocate(100);
         RandomAccessFile afile = null;
         RandomAccessFile bfile = null;
         ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
         try {
             afile = new RandomAccessFile("hello.txt", "r");
             bfile = new RandomAccessFile("hehe.txt", "rw");
             readWriteLock.readLock().lock();
             FileChannel fileChannel = afile.getChannel();
             ByteBuffer[] buffers = {head, body};
             while (fileChannel.read(buffers) != -1){
             }
             head.flip();
             body.flip();
             System.out.println(new String(head.array()));
             System.out.println(new String(body.array()));
             readWriteLock.readLock().unlock();
             fileChannel.close();
             afile.close();
 
             readWriteLock.writeLock().lock();
             FileChannel bfileChannel = bfile.getChannel();
 
             while (bfileChannel.write(buffers) > 0){
             }
 
             readWriteLock.writeLock().unlock();
             bfileChannel.close();
             bfile.close();
         }catch (Exception e){
             e.printStackTrace();
         }
     }

带offset、length参数重载read write方法，指明从那个buffer开始，共使用多少个buffer。