nio之channel

Java NIO的通道类似流，但又有些不同：

• 既可以从通道中读取数据，又可以写数据到通道。但流的读写通常是单向的。
• 通道可以异步地读写。
• 通道中的数据总是要先读到一个Buffer，或者总是要从一个Buffer中写入。

正如上面所说，从通道读取数据到缓冲区，从缓冲区写入数据到通道。如下图所示：

下面是一个用nio的channel读文件的例子

public static void nioReadFile() throws IOException {
        System.out.println("nio begin");
        RandomAccessFile raf = new RandomAccessFile("D:\\test1.txt","rw");
        RandomAccessFile rafc = new RandomAccessFile("D:\\test1.txt","rw");
        //读取通道
        FileChannel fc = raf.getChannel();
        System.out.println("beg1:  " + fc.size());
        FileChannel fc2 = rafc.getChannel();
        System.out.println("beg2:  " + fc2.size());

        ByteBuffer buffer =  ByteBuffer.allocate(150);
        ByteBuffer buffer1 =  ByteBuffer.allocate(150);
        //j将channel读入buffer
        int by = fc.read(buffer);
        System.out.println("beg:  " + fc.size());

        int byd = fc2.read(buffer1);
        System.out.println("beg213:  " + byd);

        while (by != -1){//-1时说明没有内容（一个chaneel只能读一次？）
            //回归position 因为之前读过一次
            buffer.flip();
            System.out.println("posi2: " + buffer.position());
            String  a = "";
            while (buffer.hasRemaining()){
               // System.out.println("ppdfdf1: " + buffer.position());
                char ab= (char)buffer.get();
                a = a + ab;
                //System.out.println(ab);
                //System.out.println("ppsdfsdf2: " + buffer.position());
            }
            System.out.println("sb:s1 "  + buffer.position());
            buffer.clear();
            by = fc.read(buffer);

        }
        raf.close();
    }

    public static  void test() throws Exception {
        //声明randowFile
        RandomAccessFile a = new RandomAccessFile("D:\\test1.txt", "rw");
        //获取channel
        FileChannel fc = a.getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(500);
        //用buffer读入channerl
        fc.read(buffer);
        //buffeer回归初始position
        buffer.flip();
        while (buffer.hasRemaining()){
            System.out.print((char)buffer.get());
        }
        fc.close();
    }