java nio SocketChannel 服务器端与多客户端 信息交互（聊天功能）

服务端代码：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class NIOSServer {
    private int port = 8888;
    
    //解码buffer  
    private Charset cs = Charset.forName("utf-8");
    
    /*接受数据缓冲区*/
    private static ByteBuffer sBuffer = ByteBuffer.allocate(1024);
    
    /*发送数据缓冲区*/
    private static ByteBuffer rBuffer = ByteBuffer.allocate(1024);
    
    /*映射客户端channel */
    private Map clientsMap = new HashMap();
    
    private static Selector selector;
    
    public NIOSServer(int port) {
        this.port = port;
        try {
            init();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    private void init() throws IOException {
        /* 
         *启动服务器端，配置为非阻塞，绑定端口，注册accept事件 
         *ACCEPT事件：当服务端收到客户端连接请求时，触发该事件 
         */
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(false);
        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocket.bind(new InetSocketAddress(port));
        selector = Selector.open();
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("server start on port:" + port);
    }
    
    /** 
     * 服务器端轮询监听，select方法会一直阻塞直到有相关事件发生或超时 
     */
    private void listen() {
        while (true) {
            try {
                selector.select();//返回值为本次触发的事件数  
                Set selectionKeys = selector.selectedKeys();
                for (SelectionKey key : selectionKeys) {
                    handle(key);
                }
                selectionKeys.clear();//清除处理过的事件  
            }
            catch (Exception e) {
                e.printStackTrace();
                break;
            }
            
        }
    }
    
    /** 
     * 处理不同的事件 
    */
    private void handle(SelectionKey selectionKey) throws IOException {
        ServerSocketChannel server = null;
        SocketChannel client = null;
        String receiveText = null;
        int count = 0;
        if (selectionKey.isAcceptable()) {
            /* 
             * 客户端请求连接事件 
             * serversocket为该客户端建立socket连接，将此socket注册READ事件，监听客户端输入 
             * READ事件：当客户端发来数据，并已被服务器控制线程正确读取时，触发该事件 
             */
            server = (ServerSocketChannel)selectionKey.channel();
            client = server.accept();
            client.configureBlocking(false);
            client.register(selector, SelectionKey.OP_READ);
        }
        else if (selectionKey.isReadable()) {
            /* 
             * READ事件，收到客户端发送数据，读取数据后继续注册监听客户端 
             */
            client = (SocketChannel)selectionKey.channel();
            rBuffer.clear();
            count = client.read(rBuffer);
            if (count > 0) {
                rBuffer.flip();
                receiveText = String.valueOf(cs.decode(rBuffer).array());
                System.out.println(client.toString() + ":" + receiveText);
                dispatch(client, receiveText);
                client = (SocketChannel)selectionKey.channel();
                //client.register(selector, SelectionKey.OP_READ);
            }
        }
    }
    
    /** 
     * 把当前客户端信息 推送到其他客户端 
     */
    private void dispatch(SocketChannel client, String info) throws IOException {
        Socket s = client.socket();
        String name =
            "[" + s.getInetAddress().toString().substring(1) + ":" + Integer.toHexString(client.hashCode()) + "]";
        if (!clientsMap.isEmpty()) {
            for (Map.Entry entry : clientsMap.entrySet()) {
                SocketChannel temp = entry.getValue();
                if (!client.equals(temp)) {
                    sBuffer.clear();
                    sBuffer.put((name + ":" + info).getBytes());
                    sBuffer.flip();
                    //输出到通道  
                    temp.write(sBuffer);
                }
            }
        }
        clientsMap.put(name, client);
    }
    
    public static void main(String[] args) throws IOException {
        NIOSServer server = new NIOSServer(7777);
        server.listen();
    }
}

客户端，可运行多个

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Date;
import java.util.Scanner;
import java.util.Set;

public class NIOSClient {
    /*发送数据缓冲区*/
    private static ByteBuffer sBuffer = ByteBuffer.allocate(1024);
    
    /*接受数据缓冲区*/
    private static ByteBuffer rBuffer = ByteBuffer.allocate(1024);
    
    /*服务器端地址*/
    private InetSocketAddress SERVER;
    
    private static Selector selector;
    
    private static SocketChannel client;
    
    private static String receiveText;
    
    private static String sendText;
    
    private static int count = 0;
    
    public NIOSClient(int port) {
        SERVER = new InetSocketAddress("localhost", port);
        init();
    }
    
    public void init() {
        try {
            /* 
              * 客户端向服务器端发起建立连接请求 
              */
            SocketChannel socketChannel = SocketChannel.open();
            socketChannel.configureBlocking(false);
            selector = Selector.open();
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
            socketChannel.connect(SERVER);
            /* 
             * 轮询监听客户端上注册事件的发生 
             */
            while (true) {
                selector.select();
                Set keySet = selector.selectedKeys();
                for (final SelectionKey key : keySet) {
                    handle(key);
                }
                ;
                keySet.clear();
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) throws IOException {
        new NIOSClient(7777);
    }
    
    private void handle(SelectionKey selectionKey) throws IOException {
        if (selectionKey.isConnectable()) {
            /* 
             * 连接建立事件，已成功连接至服务器 
             */
            client = (SocketChannel)selectionKey.channel();
            if (client.isConnectionPending()) {
                client.finishConnect();
                System.out.println("connect success !");
                sBuffer.clear();
                sBuffer.put((new Date() + " connected!").getBytes());
                sBuffer.flip();
                client.write(sBuffer);//发送信息至服务器  
                /* 原文来自站长网
                 * 启动线程一直监听客户端输入，有信息输入则发往服务器端 
                 * 因为输入流是阻塞的，所以单独线程监听 
                 */
                new Thread() {
                    @Override
                    public void run() {
                        while (true) {
                            try {
                                sBuffer.clear();
                                Scanner cin = new Scanner(System.in);
                                sendText = cin.nextLine();
                                System.out.println(sendText);
                                /* 
                                 * 未注册WRITE事件，因为大部分时间channel都是可以写的 
                                 */
                                sBuffer.put(sendText.getBytes("utf-8"));
                                sBuffer.flip();
                                client.write(sBuffer);
                            }
                            catch (IOException e) {
                                e.printStackTrace();
                                break;
                            }
                        }
                    };
                }.start();
            }
            //注册读事件  
            client.register(selector, SelectionKey.OP_READ);
        }
        else if (selectionKey.isReadable()) {
            /* 
             * 读事件触发 
             * 有从服务器端发送过来的信息，读取输出到屏幕上后，继续注册读事件 
             * 监听服务器端发送信息 
             */
            client = (SocketChannel)selectionKey.channel();
            rBuffer.clear();
            count = client.read(rBuffer);
            if (count > 0) {
                receiveText = new String(rBuffer.array(), 0, count);
                System.out.println(receiveText);
                client = (SocketChannel)selectionKey.channel();
                client.register(selector, SelectionKey.OP_READ);
            }
        }
    }
}

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