用java.net进行UDP编程服务器端和客户端的流程是怎样的?

服务器端：
import java.io.*;
import java.net.*;
import java.applet.Applet;
public class TalkServer{
public static void main(String args[]) {
try{
ServerSocket server=null;
try{
server=new ServerSocket(4700);
}catch(Exception e) {
System.out.println("can not listen to:"+e);
}
Socket socket=null;
try{
socket=server.accept();
}catch(Exception e) {
System.out.println("Error."+e);
}
String line;
BufferedReader is=new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter os=new PrintWriter(socket.getOutputStream());
BufferedReader sin=new BufferedReader(new InputStreamReader(System.in));
System.out.println("Client:"+is.readLine());
line=sin.readLine();
while(!line.equals("bye")){
os.println(line);
os.flush();
System.out.println("Server:"+line);
System.out.println("