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[英]How can I use UDP in JAVA Socket Programming to implement simple message communication between two ports?
[英]How can I listen to UDP ports in Java?
我必須在我的Java項目中為UDP監聽3個不同的端口。 我按如下方式實現了我的系統:
我有一個實現Runnable的UDPMessageListener類。 我想創建3個作為此對象運行的線程。
我有一個名為“ UDPPacketProcessor ”的接口,它有一個onPacketReceived方法。
每個UDPMessageListener都有一個UDPPacketProcessor實例,並將UDP數據包定向到注冊為其UDPPacketProcessor的對象。
我有一個DatabaseProc類需要服務於來自3個不同UDP端口的消息。 DatabaseProc實現UDPPacketProcessor以將自身注冊到這3個UDPMessageListener類。
從理論上講,根據我的Java知識,沒有任何問題,3個Runnable線程監聽3個端口,並且在收到數據包時,調用我的主單例對象方法的方法。 但是,當我運行程序時, 只會偵聽其中一個端口。 我只能HBMessageListener正常工作,其他人不響應。 當我繞過HBMessageListener(注釋掉我運行它的行)時,我現在可以看到只有AlarmMessageListener工作。 我哪里錯了?
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 + "!");
}
}
問題出在DatabaseProc
類中。 將runListeners
更改為如下所示。
private void runListeners(){
new Thread(HBMessageListener).start();
new Thread(AlarmMessageListener).start();
new Thread(TrackMessageListener).start();
}
編輯
解釋是直接調用UDPMessageListener.run()
時,它不是創建新線程並異步執行。 使用您的代碼,執行將永遠不會出現在HBMessageListener.run()
方法中,因為它處於無限循環中。 您需要並行化監聽器,以便所有人都可以收聽。
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