TCP通信——端口转发（重点内容）

实现多人群聊

Client(客户端）建立通信

package com.zz.tcp.case1;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
import java.util.Scanner;

public class Client {
    public static void main(String args[]) throws Exception {
        //1.创建Socket对象，并同时请求与服务端程序连接
        Socket socket = new Socket("127.0.0.1", 8888);

        //创建一个独立的线程，负责随机从socket中接收服务端的发送过来的消息
        new ClientReaderThread(socket).start();

        //2.从socket通信管道中的到一个字节输出流，用来发送数据
        OutputStream os = socket.getOutputStream();

        //将低级的字节输出流包装成数据输出流
        DataOutputStream dos = new DataOutputStream(os);

        Scanner sc = new Scanner(System.in);
        while(true){
            System.out.println("请说：");
            String msg = sc.nextLine();

            //一旦用户输入了exit就退出客户端程序
            if("exit".equals(msg)){
                System.out.println("欢迎您下次光临！");
                dos.close();
                socket.close();
                break;
            }

            //4.开始写数据出去
            dos.writeUTF(msg);
            //5.刷新数据，防止数据留在管道
            dos.flush();
        }
    }
}

ClientReaderThread（服务端线程类）——实现接收服务端转发的消息

package com.zz.tcp.case1;

import java.io.*;
import java.net.Socket;

public class ClientReaderThread extends Thread{
    private Socket socket;
    public ClientReaderThread(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try {
            InputStream is = socket.getInputStream();
            DataInputStream dis = new DataInputStream(is);
            while (true) {
                try {
                    String msg = dis.readUTF();
                    System.out.println(msg);
                    //把这个消息发送给全部客户端进行接收
                    sendMsgToAll(msg);
                } catch (Exception e) {
                    System.out.println("自己下线了" + socket.getRemoteSocketAddress());
                    dis.close();
                    socket.close();
                    break;
                }

            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void sendMsgToAll(String msg) throws IOException {
        //发送给全部在线的socket的管道接收
        for (Socket onLineSocket: Server.onLineSockets) {
            OutputStream os = onLineSocket.getOutputStream();
            DataOutputStream dos = new DataOutputStream(os);

            dos.writeUTF(msg);
            dos.flush();
        }
    }
}

Server（服务端）负责接收客户端的消息，通过8888端口建立连接

package com.zz.tcp.case1;

import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class Server {
    public static List<Socket> onLineSockets = new ArrayList <>();
    public static void main(String args[]) throws Exception{
        System.out.println("========服务端启动========");
        //1.创建ServerSocket的对象，调用一个accept方法，等待客户端的连接请求
        ServerSocket serverSocket = new ServerSocket(8888);
        while (true){
            //2.使用ServerSocket对象，调用一个accept方法，等待客户端的连接请求
            Socket socket = serverSocket.accept();
            onLineSockets.add(socket);
            System.out.println("有人上线了" + socket.getRemoteSocketAddress());
            //3.把这个客户端对应的socket通信管道，交给一个独立的线程复制处理
            new ServerReaderThread(socket).start();
        }

    }
}

ServerReaderThread（客户端线程类）——负责接受客户端发的消息，然后转发给其他客户端

package com.zz.tcp.case1;

import java.io.*;
import java.net.Socket;

public class ServerReaderThread extends Thread{
    private Socket socket;
    public ServerReaderThread(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try {
            InputStream is = socket.getInputStream();
            DataInputStream dis = new DataInputStream(is);
            while (true) {
                try {
                    String msg = dis.readUTF();
                    System.out.println(msg);
                    //把这个消息发送给全部客户端进行接收
                    sendMsgToAll(msg);
                } catch (Exception e) {
                    System.out.println("有人下线了" + socket.getRemoteSocketAddress());
                    Server.onLineSockets.remove(socket);
                    dis.close();
                    socket.close();
                    break;
                }

            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void sendMsgToAll(String msg) throws IOException {
        //发送给全部在线的socket的管道接收
        for (Socket onLineSocket: Server.onLineSockets) {
            OutputStream os = onLineSocket.getOutputStream();
            DataOutputStream dos = new DataOutputStream(os);

            dos.writeUTF(msg);
            dos.flush();
        }
    }
}