Java简易版：UDP协议实现群聊

要先运行服务端，在运行客户端，否则会报错。

服务端：

package 二十一章;



import java.io.*;
import java.net.*;
import java.util.ArrayList;
public class T{
   public static ServerSocket server_socket;
   public static ArrayList<Socket> socketList=new ArrayList<Socket>();  
   public static void main(String []args){
       try{
           server_socket = new ServerSocket(5000);
           while(true){
               Socket socket = server_socket.accept();
               socketList.add(socket); //把sock对象加入sock集合
               ServerBO_Thread st=new ServerBO_Thread(socket,socketList); //初始化多线程
               st.start();//启动多线程
           }
       }catch(Exception ex){
           ex.printStackTrace();
       }finally{
           try{
               if(server_socket!=null){
                   server_socket.close();
               }
           }catch(Exception ex){
               ex.printStackTrace();
           }
       }
   }
   public void encryptWrite(String src,DataOutputStream output)throws IOException{
       //将一个字符串转化为字符数组
       //System.out.println(src);
       char[] char_arr = src.toCharArray();
       //加密操作
       for(int i = 0;i<char_arr.length;i++){
           output.writeChar(char_arr[i]+13);
       }
       //用作结束标志符
       output.writeChar(2333);
       output.flush();
   }
   //读取并解密
   public String readDecrypt(DataInputStream input)throws IOException{
       String rtn="";
       while(true){
           int char_src =input.readChar();
           if(char_src!=2333){
               rtn=rtn+(char)(char_src-13);
           }else{
               break;
           }
       }
       return rtn;
   }
}
class ServerBO_Thread extends Thread{
   Socket client = null;
   ArrayList<Socket> clients;
   ServerBO_Thread(Socket s,ArrayList<Socket> ss){//初始化
       client=s;
       clients=ss; 
   }
   public void run(){
       DataInputStream input = null;
       DataOutputStream output =null;
       try{
           input = new DataInputStream(client.getInputStream());
           T bo = new T();
           String receive=null;
           String send=null;
           while(true){//监视当前客户端有没有发来消息
               if(!client.isClosed()){
                   receive=bo.readDecrypt(input);
                   clients.trimToSize();
                   String[] param = receive.split("&");
                   if(")start".equals(param[1])){    //分析客户端发来的内容
                       send = param[0]+"进入聊天室";
                   }else{
                       send = param[0]+"说:    "+param[1];
                   }
                   if(!("3333".equals(param[1]))){//3333为退出聊天室信号
                       for(Socket socket:clients){ //遍历socke集合 
                           //把读取到的消息发送给各个客户端  
                           if(!socket.isClosed()){
                               output = new DataOutputStream(socket.getOutputStream());
                               bo.encryptWrite(send,output);
                           }
                       }  
                   }else{//如果有客户端退出
                       for(Socket socket:clients){ //遍历socke集合 
                               if(socket!=client){//告诉其他人此人退出聊天室
                                   if(!(socket.isClosed())){
                                       output = new DataOutputStream(socket.getOutputStream());
                                       bo.encryptWrite(param[0]+"已退出聊天室",output);
                                   }
                               }
                           }
                       output = new DataOutputStream(client.getOutputStream());
                       bo.encryptWrite("3333",output);//返回信号给要退出的客户端，然后关闭线程
                       client.close();
                       input.close();
                       output.close();
                   }
               }else{
                   break;
               }
           }
       }catch(Exception ex){
           ex.printStackTrace();
       }
   }
}

客户端：

package 二十一章;


import java.io.IOException;
import java.util.Scanner;
import java.net.*;
import java.io.*;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.DataOutputStream;
public class People{
//服务端ip
   public  String ip = "127.0.0.1";
   //服务端端口
   public  int port = 5000;
   public  DataOutputStream output = null;
   public  Socket socket = null;
   public  DataInputStream input = null;
   public  Scanner sc =new Scanner (System.in);
   public  String send ;
   public  String receive;
   public  String name;
   public String sd = null;
   public static void main(String[]aa){
       People po = new People();
       po.start();
   }
   public void start(){
       try{
           System.out.println("*******欢迎使用匿名聊天室！**********");
           System.out.println("请输入你将要使用的昵称：");
           name=sc.nextLine();//获取昵称
           socket = new Socket(ip,port);
           output=new DataOutputStream(socket.getOutputStream());
           input = new DataInputStream(socket.getInputStream());
           send = name+"&)start";//把昵称发送到server 告诉所有人有新成员加入聊天室
           System.out.println("(如果要退出聊天室请输入“3333”！)");
           System.out.println("*******成功进入匿名聊天室！**********");
           System.out.println("");
           encryptWrite(send,output);
           Out out=new Out(output,name,input,socket);
           out.start();//启动发送聊天内容的多线程
           while(true){    
               String receive = readDecrypt(input);
               if("3333".equals(receive)){//如果收到“3333”则退出聊天室
                   System.out.println("*******成功退出匿名聊天室！**********");
                   input.close();
                   output.close();
                   socket.close();
                   System.exit(0);
               }
               System.out.println(receive);
           }
       }catch(Exception ex){
               ex.printStackTrace();
       }finally{
           try{
               if(socket!=null) socket.close();
               input.close();
               output.close();
           }catch(Exception ex){
               ex.printStackTrace();
           }
       }    
   }
   public void encryptWrite(String src,DataOutputStream output)throws IOException{
       //将一个字符串转化为字符数组
       char[] char_arr = src.toCharArray();
       //加密操作
       for(int i = 0;i<char_arr.length;i++){
           output.writeChar(char_arr[i]+13);
       }
       //用作结束标志符
       output.writeChar(2333);
       output.flush();
   }
   //读取并解密
   public String readDecrypt(DataInputStream input)throws IOException{
       String rtn="";
       while(true){
           int char_src =input.readChar();
           if(char_src!=2333){
               rtn=rtn+(char)(char_src-13);
           }else{
               break;
           }
       }
       return rtn;
   }
}
class Out extends Thread {
   public DataOutputStream output;
   public DataInputStream input;
   public static String name;
   public Socket socket;
   public  Scanner sc =new Scanner (System.in);
   Out(DataOutputStream ot,String n,DataInputStream it,Socket socket){
       output=ot;
       input=it;
       name=n;
   }
   public void run(){
       People po = new People();
       try{
           while(true){
               String send=sc.nextLine();//获取用户输入
               String send2=name+"&"+send;//把聊天内容打包成约定形式
               po.encryptWrite(send2,output);
           }
       }catch(Exception ex){
           ex.printStackTrace();
       }finally{
           System.out.println("sfef");
       }
   }
}

运行结果：