Java Socket编程实例（二）- UDP基本使用_java

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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