java实现udp通讯的代码

需求：应用A（通常有多个）和应用B（1个）进行 socket通讯，应用A必须知道应用B的ip地址（在应用A的配置文件中写死的），这个时候就必须把应用B的ip设成固定ip（但是某些时候如更换路由后要重新设置网络，但是操作人员不知道这个规则），就有可能造成应用A和应用B无法进行正常通讯，所以要改成应用A动态获取应用B的ip地址。

经过讨论决定采用udp协议实现，upd是一种无连接的传输层协议。应用A在不知道应用B的 ip情况下 可以使用广播地址255.255.255.255，将消息发送到在同一广播网络上的B。从而获取B的ip。

实现代码：

B应用为服务端：将udp监听放到一个线程中，当有客户端请求时就会进行响应

public class UdpServer extends Thread implements Runnable {
  private final int MAX_LENGTH = 1024;
  private final int PORT = 5060;
  private DatagramSocket datagramSocket;
  
  public void run() {
    try {
      init();
      while(true){
 try {
   byte[] buffer = new byte[MAX_LENGTH];
   DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
   receive(packet);
   String receStr = new String(packet.getData(), 0 , packet.getLength());
   System.out.println("接收数据包" + receStr);
   byte[] bt = new byte[packet.getLength()];
   
   System.arraycopy(packet.getData(), 0, bt, 0, packet.getLength());
   System.out.println(packet.getAddress().getHostAddress() + "：" + packet.getPort() + "：" + Arrays.toString(bt));
   packet.setData(bt);
   response(packet);
   
 } catch (Exception e) {
   e.printStackTrace();
   LoggerUtil.error("udp线程出现异常：" + e.toString());
 }
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  public void receive(DatagramPacket packet) throws Exception {
    datagramSocket.receive(packet);
  }

  public void response(DatagramPacket packet) throws Exception {
    datagramSocket.send(packet);
  }
  
  
  public void init(){
    try {
      datagramSocket = new DatagramSocket(PORT);
      System.out.println("udp服务端已经启动！");
    } catch (Exception e) {
      datagramSocket = null;
      System.out.println("udp服务端启动失败！");
      e.printStackTrace();
    }
  }
}

客户端：本来客户端是使用pb来实现的，但是这里使用java来模拟

public class UdpClient {
  
  private String sendStr = "hello";
  private String netAddress = "255.255.255.255";
  private final int PORT = 5060;
  
  private DatagramSocket datagramSocket;
  private DatagramPacket datagramPacket;
  
  public UdpClient(){
    try { 
      datagramSocket = new DatagramSocket();
      byte[] buf = sendStr.getBytes();
      InetAddress address = InetAddress.getByName(netAddress);
      datagramPacket = new DatagramPacket(buf, buf.length, address, PORT);
      datagramSocket.send(datagramPacket);
      
      byte[] receBuf = new byte[1024];
      DatagramPacket recePacket = new DatagramPacket(receBuf, receBuf.length);
      datagramSocket.receive(recePacket);
      
      String receStr = new String(recePacket.getData(), 0 , recePacket.getLength());
      
　　　　　　　//获取服务端ip
      String serverIp = recePacket.getAdress();
    } catch (SocketException e) {
      e.printStackTrace();
    } catch (UnknownHostException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      // 关闭socket
      if(datagramSocket != null){
 datagramSocket.close();
      }
    }
  }
  
  public static void main(String[] args) {
    for (int i = 0; i < 100; i++) {
      new Thread(new Runnable() {
 @Override
 public void run() {
   UdpClient udpClient = new UdpClient();
 }
      }).start();
    }
  }
}

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