Java Socket编程实例（二）- UDP基本使用

一.服务端代码：

import java.io.*; 
import java.net.*; 
 
public class udpechoserver { 
 
  private static final int echomax = 255; // maximum size of echo datagram 
 
  public static void main(string[] args) throws ioexception { 
 
    int servport = 5500; // server port 
 
    datagramsocket socket = new datagramsocket(servport); 
    datagrampacket packet = new datagrampacket(new byte[echomax], echomax); 
 
    while (true) { // run forever, receiving and echoing datagrams 
      socket.receive(packet); // receive packet from client 
      system.out.println("handling client at " + packet.getaddress().gethostaddress() + " on port " + packet.getport()); 
      socket.send(packet); // send the same packet back to client 
      packet.setlength(echomax); // reset length to avoid shrinking buffer 
    } 
    /* not reached */ 
  } 
} 

二.客户端代码：

import java.net.*; 
import java.io.*; 
 
public class udpechoclienttimeout { 
 
  private static final int timeout = 3000; // resend timeout (milliseconds) 
  private static final int maxtries = 5; // maximum retransmissions 
 
  public static void main(string[] args) throws ioexception { 
    inetaddress serveraddress = inetaddress.getbyname("127.0.0.1"); // server address 
    int servport = 5500; // server port 
    // convert the argument string to bytes using the default encoding 
    byte[] bytestosend = "hi, world".getbytes(); 
 
    datagramsocket socket = new datagramsocket(); 
    socket.setsotimeout(timeout); // maximum receive blocking time(milliseconds) 
    // sending packet 
    datagrampacket sendpacket = new datagrampacket(bytestosend, bytestosend.length, serveraddress, servport); 
 
    datagrampacket receivepacket = // receiving packet 
    new datagrampacket(new byte[bytestosend.length], bytestosend.length); 
 
    int tries = 0; // packets may be lost, so we have to keep trying 
    boolean receivedresponse = false; 
    do { 
      socket.send(sendpacket); // send the echo string 
      try { 
        socket.receive(receivepacket); // attempt echo reply reception 
 
        if (!receivepacket.getaddress().equals(serveraddress)) {// check 
                                    // source 
          throw new ioexception("received packet from an unknown source"); 
        } 
        receivedresponse = true; 
      } catch (interruptedioexception e) { // we did not get anything 
        tries += 1; 
        system.out.println("timed out, " + (maxtries - tries) + " more tries..."); 
      } 
    } while ((!receivedresponse) && (tries < maxtries)); 
 
    if (receivedresponse) { 
      system.out.println("received: " + new string(receivepacket.getdata())); 
    } else { 
      system.out.println("no response -- giving up."); 
    } 
    socket.close(); 
  }
} 

上述代码的udp服务端是单线程，一次只能服务一个客户端。

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