Java 非阻塞式NIO 案例（实现多人聊天功能）

一、使用Java NIO完成网络通信的三个核心

　　1.通道（Channel）：负责连接

　　      java.nio.channels.Channel 接口：
              |--SelectableChannel
                  |--SocketChannel
                  |--ServerSocketChannel
                  |--DatagramChannel
 
                  |--Pipe.SinkChannel
                  |--Pipe.SourceChannel

　　2.缓冲区（buffer）：负责数据存取

　　3.选择器（Selector）:是SelectableChannel 的多路复用器，用来检测SelectableChannel的IO状态

案例：使用非阻塞式实现简单的群聊天系统

一、实现客户端

    public static void main(String[] args) throws Exception {
        SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 8989));

        //2. 切换非阻塞模式
        sChannel.configureBlocking(false);

        //3. 分配指定大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);

        //4. 发送数据给服务端
        Scanner scan = new Scanner(System.in);

        while (scan.hasNext()) {
            String str = scan.next();
            buf.put((new Date().toString() + "
" + str).getBytes());
            buf.flip();
            sChannel.write(buf);
            buf.clear();
        }

        //5. 关闭通道
        sChannel.close();
    }

二、实现服务端

    @Test
    public void server() {
        ServerSocketChannel ssChannel = null;
        try {
            ssChannel = ServerSocketChannel.open();
            //配置非阻塞
            ssChannel.configureBlocking(false);
            //绑定连接
            ssChannel.bind(new InetSocketAddress(8989));

            Selector selector = Selector.open();

            //将通道注册到监听器中，并且制定监听器的监听模式为“接受”
            ssChannel.register(selector, SelectionKey.OP_ACCEPT);

            //轮询的选择已经就绪的事件
            while (selector.select() > 0) {
                //获取当前监听
                Iterator<SelectionKey> it = selector.selectedKeys().iterator();

                while (it.hasNext()) {
                    //获取准备就绪的事件
                    SelectionKey sk = it.next();
                    if (sk.isAcceptable()) {
                        //如果接受就绪，则获取客户端的连接
                        SocketChannel clientChannel = ssChannel.accept();

                        //同样配置成非阻塞式
                        clientChannel.configureBlocking(false);

                        //把客户端的连接注册到选择器上
                        clientChannel.register(selector, SelectionKey.OP_READ);
                    } else if (sk.isReadable()) {
                        //如果读取就绪，则获取读取的通道
                        SocketChannel socketChannel = (SocketChannel) sk.channel();

                        //配置成非阻塞模式
                        socketChannel.configureBlocking(false);

                        //读取数据

                        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

                        int len = 0;
                        while ((len = socketChannel.read(byteBuffer)) > 0) {
                            byteBuffer.flip();
                            System.out.println(new String(byteBuffer.array(), 0, len));
                            byteBuffer.clear();
                        }
                    }
                    it.remove();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(ssChannel!=null){
                try {
                    ssChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

注意：这里服务端用到的org.junit.Test;这个包方便测试，客户端因为需要读取输入所以写在Main函数中（@Test方法中测试出来好像不能读取输入）

需要下载包的地址如下：

链接：https://pan.baidu.com/s/14ZHHOnAD3ldNVcA3pmCoJQ
提取码：uqd9

DatagramChannel（UDP）的使用方法（和上个案例大同小异）

public static void main(String args[]) {
        DatagramChannel datagramChannel = null;
        try {
            datagramChannel = DatagramChannel.open();

            datagramChannel.configureBlocking(false);

            ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

            Scanner scanner = new Scanner(System.in);

            while (scanner.hasNext()) {
                String str = scanner.next();
                byteBuffer.put(str.getBytes());
                byteBuffer.flip();
                datagramChannel.send(byteBuffer, new InetSocketAddress("127.0.0.1", 9897));
                byteBuffer.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            if(datagramChannel!=null){
                try {
                    datagramChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Test
    public void server(){
        DatagramChannel datagramChannel = null;
        try {
            datagramChannel=DatagramChannel.open();
            datagramChannel.bind(new InetSocketAddress(9897));

            datagramChannel.configureBlocking(false);

            Selector selector = Selector.open();
            datagramChannel.register(selector, SelectionKey.OP_READ);

            while(selector.select()>0){
                Iterator<SelectionKey> st=selector.selectedKeys().iterator();

                while(st.hasNext()){
                    SelectionKey sk=st.next();

                    if(sk.isReadable()){
                        ByteBuffer btf=ByteBuffer.allocate(1024);

                        datagramChannel.receive(btf);

                        btf.flip();

                        System.out.println(new String(btf.array(),0,btf.limit()));
                        btf.clear();
                    }
                }
                st.remove();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(datagramChannel!=null){
                try {
                    datagramChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

Pipe简介

pipe是两个线程之间单项数据连接，Pipe有两个数据通道，Sign通道负责写入，Source通道负责读取。
案例如下：

    @Test
    public void test() throws Exception {
        Pipe pipe = Pipe.open();

        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

        byteBuffer.put("hello world".getBytes());

        Pipe.SinkChannel sinkChannel=pipe.sink();
        byteBuffer.flip();
        sinkChannel.write(byteBuffer);


        //读取

        Pipe.SourceChannel sourceChannel =pipe.source();
        byteBuffer.flip();
        int len=sourceChannel.read(byteBuffer);

        System.out.println("sourceChanel:"+new String(byteBuffer.array(),0,len));
        byteBuffer.clear();

        sinkChannel.close();

        sourceChannel.close();

    }

谢谢浏览，如有问题直接评论，我会及时更改我的错误。