import java.net.*; 
import java.io.*; 
import java.lang.*; 

public class myserver{ 
public static void main(String args[]){ 
ServerSocket server; 
Socket socket; 
String s; 
InputStream Is; 
OutputStream Os; 
DataInputStream DIS; 
PrintStream PS; 

try{ 
//在端口4321注册服务 
server=new ServerSocket(4321); 
socket=server.accept(); 　　//监听窗口,等待连接   

System.out.println("server ok"); 
System.out.println("************************************************"); 
System.out.println(""); 

//获得对应Socket的输入/输出流 
Is=socket.getInputStream(); 
Os=socket.getOutputStream(); 
//建立数据流 
DIS=new DataInputStream(Is); 
PS=new PrintStream(Os); 
DataInputStream in=new DataInputStream(System.in); 
while(true){ 
System.out.println(""); 
System.out.println("please wait client's message..."); 
System.out.println(""); 
s=DIS.readLine(); //读入从client传来的字符串 
System.out.println("client said:"+s); //打印字符串 
if(s.trim().equals("BYE"))break; //如果是"BYE",就退出 
System.out.print("you say:"); 
s=in.readLine(); //读取用户输入的字符串 
PS.println(s); //将读取得字符串传给client 
if(s.trim().equals("BYE"))break; //如果是"BYE",就退出 

} 

//关闭连接 
DIS.close(); //关闭数据输入流 
PS.close(); //关闭数据输出流 
Is.close(); //关闭输入流 
Os.close(); //关闭输出流 
socket.close(); //关闭sockey 
} 
catch(Exception e){ 
System.out.println("Error:"+e); 
} 
} 
}