java - 我如何在 Java 中监听 UDP 端口？

Question

我必须在我的 Java 项目中监听 3 个不同的 UDP 端口。我按如下方式实现了我的系统:

我有一个实现 Runnable 的 UDPMessageListener 类。我想创建 3 个线程作为这个对象运行。

我有一个名为“UDPPacketProcessor”的接口(interface)，它有一个 onPacketReceived 方法。

每个 UDPMessageListener 都有一个 UDPPacketProcessor 实例，并将 UDP 数据包定向到注册为其 UDPPacketProcessor 的对象。

我有一个 DatabaseProc 类，它需要处理来自 3 个不同 UDP 端口的消息。 DatabaseProc 实现 UDPPacketProcessor将自己注册到这 3 个 UDPMessageListener 类。

理论上，根据我的 Java 知识，不会有任何问题，3 个 Runnable 线程监听 3 个端口，并在收到数据包时调用我的主要单例对象方法的方法。但是，当我运行该程序时，只有一个 端口被监听。我只能 HBMessageListener 正常工作，其他的没有响应。当我绕过 HBMessageListener(注释掉我运行它的行)时，我现在可以看到只有 AlarmMessageListener 有效。我哪里错了？

UDPMessageListener.java

public class UDPMessageListener implements Runnable {

int port;
byte[] receiveData;
DatagramSocket udpListeningSocket;
UDPPacketProcessor processor;
public UDPMessageListener(UDPPacketProcessor listener,int localPort){
    port = localPort;
    this.processor = listener;
    receiveData = new byte[SRPDefinitions.BYTE_BUFFER_MAX_LENGTH];
    try {
        udpListeningSocket = new DatagramSocket(port);
    } catch (SocketException e) {
        System.out.println("Socket bind error in port: " + port);
        e.printStackTrace();
    }
}

@Override
public void run() {
    while(true){
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        try {
            udpListeningSocket.receive(receivePacket);
            System.out.println("Received UDP Packet from Port:" + port);
            processor.onPacketReceived(receivePacket, port);

        } catch (IOException e) {
            System.out.println("UDP Listener end up with an exception:");
            e.printStackTrace();
        }

    }
}
}

UDPPacketProcessor.java

public interface UDPPacketProcessor {
public void onPacketReceived(DatagramPacket receivedPacket,int localPort);
}

DatabaseProc.java

public class DatabaseProc implements UDPPacketProcessor{

private static DatabaseProc instance = null; // for singleton.

byte[] receiveData;
byte[] sendData;
ByteBuffer systemMessageByteBuffer;

UDPMessageListener HBMessageListener;
UDPMessageListener AlarmMessageListener;
UDPMessageListener TrackMessageListener;

private DatabaseProc(){
    receiveData = new byte[SRPDefinitions.BYTE_BUFFER_MAX_LENGTH];
    sendData = new byte[SRPDefinitions.BYTE_BUFFER_MAX_LENGTH];
    HBMessageListener = new UDPMessageListener(this,SRPDefinitions.HB_PORT);
    AlarmMessageListener = new UDPMessageListener(this,SRPDefinitions.ALARM_PORT);
    TrackMessageListener = new UDPMessageListener(this,SRPDefinitions.TRACK_PORT);
}

public void run(){
    runListeners();
}

private void runListeners(){
    HBMessageListener.run();
    AlarmMessageListener.run();
    TrackMessageListener.run();
}

public static DatabaseProc getInstance(){
    if(instance == null){
        instance = new DatabaseProc();
    }
    return instance;
}

@Override
public void onPacketReceived(DatagramPacket receivedPacket, int localPort) {
    String strIPAddress =receivedPacket.getAddress().toString();

    ByteBuffer buffer = ByteBuffer.allocate(receivedPacket.getLength());
    System.out.println("Received Packet Length: " + receivedPacket.getLength() + "/" + receivedPacket.getData().length);
    buffer.order(ByteOrder.LITTLE_ENDIAN);

    buffer.put(receivedPacket.getData(),0,receivedPacket.getLength());
    buffer.position(0);

    if(localPort == SRPDefinitions.HB_PORT){
        System.out.println("HB Message Received from " + strIPAddress + "!");
        SRPHeartBeatMessage message = new SRPHeartBeatMessage(buffer);
        //message.print();
    }
    if(localPort == SRPDefinitions.ALARM_PORT){
        System.out.println("ALARM Message Received from " + strIPAddress + "!");
        SRPAlarmMessage message = new SRPAlarmMessage(buffer);
        message.print();
    }
    if(localPort == SRPDefinitions.TRACK_PORT){
        System.out.println("TRACK Message Received from " + strIPAddress + "!");
    }   
}

Answer 1

问题出在 DatabaseProc 类中。将 runListeners 更改为如下所示。

private void runListeners(){
    new Thread(HBMessageListener).start();
    new Thread(AlarmMessageListener).start();
    new Thread(TrackMessageListener).start();
}

编辑

说明是直接调用UDPMessageListener.run()时，并不是新建Thread异步执行。使用您的代码，执行永远不会从 HBMessageListener.run() 方法中出来，因为它处于无限循环中。您需要并行化 Listeners，以便所有人都能收听。