教你怎么用java實現(xiàn)客戶端與服務器一問一答

更新時間：2021年04月30日 10:39:18 作者：小樓夜聽雨QAQ

這篇文章主要介紹了教你怎么用java實現(xiàn)客戶端與服務器一問一答,文中有非常詳細的代碼示例,對正在學習java的小伙伴們有非常好的幫助,需要的朋友可以參考下

運行效果

開啟多個客戶端

服務端效果：

客戶端效果：

當一個客戶端斷開連接：

代碼

因為代碼中有注釋，我就直接貼上來了

服務端：

package com.dayrain.server;
 
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.charset.StandardCharsets;
import java.util.Iterator;
 
public class NioServer {
    /**端口**/
    private static final int PORT = 8081;
    /**buffer大小**/
    private static final int DEFAULT_BUFFER_SIZE = 1024;
    private final Selector selector;
    private final ByteBuffer readBuffer = ByteBuffer.allocate(NioServer.DEFAULT_BUFFER_SIZE);
    private final ByteBuffer writeBuffer = ByteBuffer.allocate(NioServer.DEFAULT_BUFFER_SIZE);
 
    private static int count = 0;
 
    public static void main(String[] args) throws IOException {
        new NioServer().start();
    }
 
    public NioServer() throws IOException {
        //創(chuàng)建一個服務端channel
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
 
        //設置為非阻塞
        serverSocketChannel.configureBlocking(false);
 
        //獲取服務器socket
        ServerSocket socket = serverSocketChannel.socket();
        //綁定ip和端口
        socket.bind(new InetSocketAddress(NioServer.PORT));
 
        //創(chuàng)建多路復用選擇器，并保持打開狀態(tài)，直到close
        selector = Selector.open();
 
        //將服務器管道注冊到selector上，并監(jiān)聽accept事件
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("server start on port: " + NioServer.PORT);
        start();
    }
 
    public void start() throws IOException {
 
        //selector是阻塞的，直到至少有一個客戶端連接。
        while (selector.select() > 0) {
            //SelectionKey是channel想Selector注冊的令牌，可以通過chancel取消（不是立刻取消，會放進一個cancel list里面，下一次select時才會把它徹底刪除）
            Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
            while (iterator.hasNext()) {
                SelectionKey selectionKey = iterator.next();
                iterator.remove();
                //當這個key的channel已經(jīng)準備好接收套接字連接
                if(selectionKey.isAcceptable()) {
                    connectHandle(selectionKey);
                }
 
                //當這個key的channel已經(jīng)準備好讀取數(shù)據(jù)時
                if(selectionKey.isReadable()) {
                    readHandle(selectionKey);
                }
            }
        }
    }
 
    /**
     * 處理連接
     * @param selectionKey
     */
    private void connectHandle(SelectionKey selectionKey) throws IOException {
        //注意，服務端用的是ServerSocketChannel，BIO中是ServerSocket
        ServerSocketChannel serverSocketChannel = (ServerSocketChannel) selectionKey.channel();
        SocketChannel socketChannel = serverSocketChannel.accept();
        if(socketChannel == null) {
            return;
        }
        socketChannel.configureBlocking(false);
        socketChannel.register(selector, SelectionKey.OP_READ|SelectionKey.OP_WRITE);
 
        System.out.println("客戶端連接成功，當前總數(shù)：" + (++count));
 
        writeBuffer.clear();
        writeBuffer.put("連接成功".getBytes(StandardCharsets.UTF_8));
        writeBuffer.flip();
        socketChannel.write(writeBuffer);
    }
 
    /**
     * 讀取數(shù)據(jù)
     * @param selectionKey
     */
    private void readHandle(SelectionKey selectionKey){
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
        try {
            readBuffer.clear();
            int read = socketChannel.read(readBuffer);
            if(read > 0) {
                readBuffer.flip();
                String receiveData = StandardCharsets.UTF_8.decode(readBuffer).toString();
 
                System.out.println("收到客戶端消息: " + receiveData);
 
                writeBuffer.clear();
                writeBuffer.put(receiveData.getBytes(StandardCharsets.UTF_8));
                writeBuffer.flip();
                socketChannel.write(writeBuffer);
            }
 
        }catch (Exception e) {
            try {
                socketChannel.close();
            } catch (IOException ioException) {
                ioException.printStackTrace();
            }
            System.out.println("客戶端斷開了連接~~");
            count--;
        }
    }
}

客戶端

package com.dayrain.client;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
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.nio.charset.StandardCharsets;
import java.util.Iterator;
 
public class NioClient {
 
    private static final int PORT = 8081;
    private static final int DEFAULT_BUFFER_SIZE = 1024;
    private final Selector selector;
    private final ByteBuffer readBuffer = ByteBuffer.allocate(NioClient.DEFAULT_BUFFER_SIZE);
    private final ByteBuffer writeBuffer = ByteBuffer.allocate(NioClient.DEFAULT_BUFFER_SIZE);
 
    public static void main(String[] args) throws IOException {
        NioClient nioClient = new NioClient();
 
        //終端監(jiān)聽用戶輸入
        new Thread(nioClient::terminal).start();
 
        //這個方法是阻塞的，要放在最后
        nioClient.start();
    }
 
    public NioClient() throws IOException {
        selector = Selector.open();
        SocketChannel socketChannel = SocketChannel.open(new InetSocketAddress(InetAddress.getLocalHost(), NioClient.PORT));
        socketChannel.configureBlocking(false);
        socketChannel.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);
    }
 
    public void start() throws IOException {
        while (selector.select() > 0) {
            Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
            while (iterator.hasNext()) {
                SelectionKey selectionKey = iterator.next();
                //拿到selectionKey后要刪除，否則會重復處理
                iterator.remove();
                if(selectionKey.isReadable()) {
                    handleRead(selectionKey);
                }
 
                //只要連接成功，selectionKey.isWritable()一直為true
                if(selectionKey.isWritable()) {
                    handleWrite(selectionKey);
                }
            }
        }
    }
 
    /**
     * 監(jiān)聽寫操作
     */
    private void handleWrite(SelectionKey selectionKey) throws IOException {
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
 
        // writeBuffer有數(shù)據(jù)就直接寫入，因為另開了線程監(jiān)聽用戶讀取，所以要上鎖
        synchronized (writeBuffer) {
            writeBuffer.flip();
            while (writeBuffer.hasRemaining()) {
                socketChannel.write(writeBuffer);
            }
            writeBuffer.compact();
        }
 
    }
 
    /**
     * 監(jiān)聽讀操作
     */
    private void handleRead(SelectionKey selectionKey) throws IOException {
        SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
        readBuffer.clear();
        socketChannel.read(readBuffer);
 
        readBuffer.flip();
        String res = StandardCharsets.UTF_8.decode(readBuffer).toString();
        System.out.println("收到服務器發(fā)來的消息： " + res);
        readBuffer.clear();
    }
 
    /**
     * 監(jiān)聽終端的輸入
     */
    private void terminal() {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        try {
            String msg;
            while ((msg = bufferedReader.readLine()) != null) {
                synchronized (writeBuffer) {
                    writeBuffer.put((msg + "\r\n").getBytes(StandardCharsets.UTF_8));
                }
            }
        }catch (Exception e) {
            e.printStackTrace();
        }
 
    }
 
}

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