java 实现udp通信

需求：应用A（一般有多个）和应用B（1个）进行 socket通信，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（可是某些时候如更换路由后要从新设置网络，可是操做人员不知道这个规则），就有可能形成应用A和应用B没法进行正常通信，因此要改为应用A动态获取应用B的ip地址。

通过讨论决定采用udp协议实现，upd是一种无链接的传输层协议。应用A在不知道应用B的 ip状况下 能够使用广播地址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
/**
 * udp链接，用于动态ip, pos向255.255.255.255：5060发送请求便可
 * **/
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);
    }
    
    /**
     * 初始化链接
     */
    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：原本客户端是使用pb来实现的，可是这里使用java来模拟
/***
 * UDP Client端
 ***/
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();
        }
    }
}