Java 非阻塞式NIO 案例（實現多人聊天功能）

一、使用Java NIO完成網路通信的三個核心

　　1.通道（Channel）：負責連接

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

　　2.緩衝區（buffer）：負責數據存取

　　3.選擇器（Selector）:是SelectableChannel 的多路復用器，用來檢測SelectableChannel的IO狀態

案例：使用非阻塞式實現簡單的群聊天系統

一、實現客戶端

 1     public static void main(String[] args) throws Exception {
 2         SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 8989));
 3 
 4         //2. 切換非阻塞模式
 5         sChannel.configureBlocking(false);
 6 
 7         //3. 分配指定大小的緩衝區
 8         ByteBuffer buf = ByteBuffer.allocate(1024);
 9 
10         //4. 發送數據給服務端
11         Scanner scan = new Scanner(System.in);
12 
13         while (scan.hasNext()) {
14             String str = scan.next();
15             buf.put((new Date().toString() + "\n" + str).getBytes());
16             buf.flip();
17             sChannel.write(buf);
18             buf.clear();
19         }
20 
21         //5. 關閉通道
22         sChannel.close();
23     }

二、實現服務端

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

            Selector selector = Selector.open();

            //將通道註冊到監聽器中，並且制定監聽器的監聽模式為“接受”
            ssChannel.register(selector, SelectionKey.OP_ACCEPT);

            //輪詢的選擇已經就緒的事件
            while (selector.select() > 0) {
                //獲取當前監聽
                Iterator<SelectionKey> it = selector.selectedKeys().iterator();

                while (it.hasNext()) {
                    //獲取準備就緒的事件
                    SelectionKey sk = it.next();
                    if (sk.isAcceptable()) {
                        //如果接受就緒，則獲取客戶端的連接
                        SocketChannel clientChannel = ssChannel.accept();

                        //同樣配置成非阻塞式
                        clientChannel.configureBlocking(false);

                        //把客戶端的連接註冊到選擇器上
                        clientChannel.register(selector, SelectionKey.OP_READ);
                    } else if (sk.isReadable()) {
                        //如果讀取就緒，則獲取讀取的通道
                        SocketChannel socketChannel = (SocketChannel) sk.channel();

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

                        //讀取數據

                        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();
                }
            }
        }
    }

註意：這裡服務端用到的org.junit.Test;這個包方便測試，客戶端因為需要讀取輸入所以寫在Main函數中（@Test方法中測試出來好像不能讀取輸入）

需要下載包的地址如下：

鏈接：https://pan.baidu.com/s/14ZHHOnAD3ldNVcA3pmCoJQ
提取碼：uqd9

DatagramChannel（UDP）的使用方法（和上個案例大同小異）

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簡介

pipe是兩個線程之間單項數據連接，Pipe有兩個數據通道，Sign通道負責寫入，Source通道負責讀取。
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);


        //讀取

        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();

    }

謝謝瀏覽，如有問題直接評論，我會及時更改我的錯誤。