//server.java import java.io.*; import sun.net.*; class 

            server extends NetworkServer //定义服务器类 {DataInputStream net_input; //定义数据输出 

            PrintStream net_output; //定义数据输入 public static void main(String args[]) { new 

            server();} public server() //运行服务器功能，并把端口设为1111 { try 

            {startServer(1111);} catch (Exception e) { System.out.println( "Unable to start 

            server."); return; } System.out.println("Waiting for clients..."); } public 

            void serviceRequest() //定义服务应答功能 { net_input = new 

            DataInputStream(clientInput); net_output = System.out; String user = read_net_input(); 

            System.out.println(user+" connected!"); while(true) { String string; 

            if((string=read_net_input( ))==null) break; //如果客户机输入NULL，中断服务 

            write_net_output(user+":"+string); } System.out.println(user+" has 

            disconnected!"); } String read_net_input() { try {return net_input.readLine();} 

            catch(IOException e) {return null;} } void write_net_output(String string) { 

            net_output.println(string); net_output.flush(); } } 客户机程序源代码： 

            //client.java import java.io.*; import sun.net.*; class client extends NetworkClient //定义客户机类 

            { DataInputStream net_input; PrintStream net_output; public static void main(String 

            args[])//获得服务器IP地址和客户机名 { if(args.length<2) { System.out.println( "To run,type: ");
            System.out.println( "java client  "); } 

            System.out.println( "Connecting..."); try {new client(args[0],args[1]);} catch 

            (Exception e) { System.out.println( "Unable to create NetworkClient."); return; 

            } } public client (String host,String username) throws IOException //与服务器链接功能 

            { super(host,1111); if(serverIsOpen()) { System.out.println( "Connected to 

            server."); net_input = new DataInputStream(System.in); net_output = serverOutput; 

            net_output.println(username); chat(); } else System.out.println("Error:Could not 

            connect to server."); } void chat() //定义信息传递函数，当输入EXIT时，中断链接 

            { String string; System.out.println( "Type EXIT to exit"); while(true) { 

            string=read_net_input(); if(string.equalsIgnoreCase("EXIT")) break; 

            write_net_output(string); } System.out.println("Disconnecting..."); 

            close_server(); System.out.println("Done!"); } String read_net_input() { try 

            {return net_input.readLine();} catch(IOException e) {return null;} } void 

            write_net_output(String string) { net_output.println(string); net_output.flush(); } void 

            close_server() { try {closeServer();} catch(Exception e) {System.out.println("Unable 

            to close server.");} } } 

            ----