java UDP编程

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一.UDP通信的基本模式

发送数据包：

（1）DatagramSocket类创建套接字： new DatagramSocket（）；不需要指定端口号码， UDP协议，系统自己选择一个端口发送出去；

（2）DatagramPacket类创建数据包：new DatagramPacket（byte[] buf ,int offset , int length ,InetAddress address , int port ）;

（3）使用 DatagramSocket 的send 函数发送出去： socket.sent(DatagramPacket p) .

接收数据包：

（1）DatagramSocket类创建套接字：new DatagramSocket（int port ） ; 指定端口号；

（2）DatagramPacket 类创建数据包：new DatagramPacket（byte[] buf , int length）;

（3）DatagramSocket 的receive（DatagramPacket p) 来接受数据包；

注： DatagramSocket 的receive（p）函数在没有数据接受的时候是堵塞的，如果没有数据receive没有堵塞，那可能是端口号被占用了。

服务器端

package Udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class EasyServer {

   private static final int port = 8998;
   private byte [] buf;
   private DatagramSocket socket ;
   private DatagramPacket packet ;

   EasyServer(){
       try {
           socket = new DatagramSocket(port);
           buf = new byte[1024];
       } catch (SocketException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
   }

   public void getMsg(){
       String s = "";
       packet = new DatagramPacket(buf, buf.length);
       while(true){
           try {
               socket.receive(packet);
               s = new String (buf);
               System.out.println("client sent to me :"+ s);

           } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }
       }

   }

   public static void main (String args []){
       new EasyServer().getMsg();
   }
}

客户端

package Udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Scanner;

public class EasyClient {

   private static final int port = 8998;
   private DatagramSocket socket ;
   private DatagramPacket packet ;
   byte buf [];


   EasyClient(){
       try {
           socket = new DatagramSocket();
           buf = new byte[1024];
       } catch (SocketException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
   }

   @SuppressWarnings("resource")
   public void senMsg(){
       Scanner scan = new Scanner(System.in);
       try {
           InetAddress add = InetAddress.getLocalHost();

           while (true){
               String s = scan.nextLine();
               buf = s.getBytes();
               packet = new DatagramPacket(buf, 0, buf.length, add, port);
               try {
                   socket.send(packet);
               } catch (IOException e) {
                   // TODO Auto-generated catch block
                   e.printStackTrace();
               }
           }

       } catch (UnknownHostException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }

   }

   public static void main (String args[]){
       new EasyClient().senMsg();
   }

}

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