java socket通信 TCP UDP

 java socket通信
TCP客户端：
import java.net.*;
import java.io.*;
public class Client {
static Socket server;
public static void main(String[] args) throws Exception {
server = new Socket(InetAddress.getLocalHost(), 23);
BufferedReader in = new BufferedReader(new InputStreamReader(server
.getInputStream()));
PrintWriter out = new PrintWriter(server.getOutputStream());
BufferedReader wt = new BufferedReader(new InputStreamReader(System.in));
while (true) {
System.out.println("想知道现在是什么时间吗？(输入任意文字表示 同意，输入end表示退出)");
String str = wt.readLine();
out.println(str);
out.flush();
if (str.equals("end")) {
break;
}
System.out.println(in.readLine());
}
server.close();
}
}

TCP服务器代码：
import java.io.*;
import java.net.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class Server {
public static void main(String[] args) throws IOException {
ServerSocket server = new ServerSocket(23);
Socket client = server.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(client
.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream());
while (true) {
String str = in.readLine();
System.out.println(str);

SimpleDateFormat f=new SimpleDateFormat("MMM dd,yyyy kk:mm:ss");
String time = f.format(new Date());

out.println("现在的时间是："+time);
out.flush();
if (str.equals("end"))
break;
}
client.close();
}
}

UDP服务器代码：
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.ServerSocket;
import java.net.SocketException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class UDPServer {
private static DatagramSocket udpSocket = null;
private static DatagramPacket packet = null;
public UDPServer() throws SocketE