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();    }