項目結構

服務端

Server.java

package tcp;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class Server {
	public static void main(String[] args) {
		//保存已連接的客戶端的集合
		List<Socket> clients = new ArrayList<Socket>();
		try {
			//6666為自己設置的端口號
			ServerSocket serversocket = new ServerSocket(6666);
			System.out.println("****服務器啟動,等待客戶端的連接****");
			while(true) {
				Socket clientSocket = serversocket.accept();
				clients.add(clientSocket);
				new ServerThread(clientSocket,clients).start();
			}
			
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

ServerThread.java

package tcp;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.List;

public class ServerThread extends Thread {
	Socket myClient;//新發消息的客戶端
	List<Socket> clients;//所有連接的的客戶端
	String clientHostname;//客戶端IP
	int clientport;//客戶端端口號
	public ServerThread(Socket myClient,List<Socket> clients) {
		super();
		this.myClient = myClient;
		this.clients = clients;
	}
	
	public void run() {
		InetSocketAddress clientAddress = (InetSocketAddress)myClient.getRemoteSocketAddress();
		clientHostname = clientAddress.getHostName();
		clientport = clientAddress.getPort();
		System.out.println("第"+clients.size()+"個客戶端:"+clientHostname+"已連接"+":"+clientport);
		try {
			String is;
			BufferedReader in = new BufferedReader(new InputStreamReader(myClient.getInputStream()));
			while((is=in.readLine())!=null) {
				System.out.println(is+"  來自"+clientHostname+":"+clientport);
				//輸出到全部客戶端
				for (Socket client:clients) {
					if(client!=null) {
						PrintWriter out = new PrintWriter(client.getOutputStream(),true);
						out.println(is+"  來自"+clientHostname+":"+clientport);
					}
				}
			}
		} catch (IOException e) {
			System.err.println(clientHostname + ":" + clientport + "退出了。");
		}
	}
}

客戶端

Client.java

package tcp;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

public class Client {
	public Client() {
		String hostName = "";
		int portNumber = 6666;
		
		try {
			Socket s = new Socket(hostName,portNumber);
			//輸出到服務器
			PrintWriter out = new PrintWriter(s.getOutputStream(),true);
			//接收服務器傳來的數據
			BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
			//鍵盤輸入此客戶端要發送的數據
			BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
			
			//發送消息的線程
			new Thread(new Runnable() {
				@Override
				public void run() {
					// TODO Auto-generated method stub
					String input;
					try {
						while((input = sin.readLine())!=null) {
							//輸出到服務器
							out.println(input);
						}
					} catch (IOException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
						System.exit(1);
					}
				}
			}).start();
			
			//接收消息的線程
			new Thread(new Runnable() {

				@Override
				public void run() {
					// TODO Auto-generated method stub
					String receiveStr;
					try {
						while((receiveStr = in.readLine())!=null) {
							System.out.println("echo: " + receiveStr);
						}
					} catch (IOException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
						System.exit(1);
					}
				}
				
			}).start();
			
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	public static void main(String[] args) {
		new Client();
	}
}

運行結果

先啟動服務器

客戶端1

客戶端2