Question

我必须在我的Java项目中为UDP监听3个不同的端口。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个作为此对象运行的线程。

我有一个名为“ UDPPacketProcessor ”的接口，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，它需要服务于来自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，没有任何问题，3个Runnable线程监听3个端口，并且在收到数据包时，调用我的主单例对象方法的方法。但是，当我运行程序时， 只会侦听一个 端口。我只能HBMessageListener正常工作，其他人不响应。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工作。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课程中。将runListeners更改为以下内容。

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

修改

解释是直接调用UDPMessageListener.run()时，它不是创建新线程并异步执行。使用您的代码，执行将永远不会出现在HBMessageListener.run()方法中，因为它处于无限循环中。您需要并行化监听器，以便所有人都可以收听。

如何在Java中侦听UDP端口？

1 个答案: