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[英]MQTT Retained messages not received when subscribing same topic from different applications at the same time
[英]Subscribing on topic. MQTT
我有以下代碼部分:
package com.company;
import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import javax.security.auth.callback.Callback;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Main implements MqttCallback {
private static String sTopic;
private static int iQos;
private static MqttClient mqttClient;
private static String sUsername;
private static Frame frame = new Frame();
public static void main(String[] args) throws MqttException {
frame.getConnect().addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
int iPort;
String sIp = frame.getBrokerAddressValue();
sUsername = frame.getUsernameValue();
try {
String broker = "tcp://"; //bridge and host
iPort = frame.getPortValue();
broker+=sIp+":"+iPort;
mqttClient = new MqttClient(broker, sUsername, new MemoryPersistence()); //URI, ClientId, Persistence
MqttConnectOptions connectOptions = new MqttConnectOptions();
connectOptions.setCleanSession(true);
System.out.println("Connecting to broker: "+broker);
mqttClient.connect();
System.out.println("Connected");
}catch (NumberFormatException exc){
System.out.println("Wrong port format");
} catch (MqttException e1) {
e1.printStackTrace();
}
}
});
frame.getSubscribe().addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
sTopic = frame.getTopicValue();
try {
mqttClient.subscribe(sTopic);
} catch (MqttException e1) {
e1.printStackTrace();
}
System.out.println("Subscribed");
}
});
frame.getPublish().addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
String sMessage = frame.getMessageValue();
MqttMessage message = new MqttMessage(sMessage.getBytes());
iQos = frame.getQosValue();
message.setQos(iQos);
try {
mqttClient.publish(sTopic,message);
} catch (MqttException e1) {
e1.printStackTrace();
}
System.out.println("Message published");
}
});
}
@Override
public void connectionLost(Throwable throwable) {
}
@Override
public void messageArrived(String topic, MqttMessage message) throws Exception{
frame.getTextArea().setText(String.valueOf(message));
}
@Override
public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
}
}
這是我實現mqtt客戶端的一部分。 方法getConnect正在處理單擊“連接”按鈕,方法getSubscribe正在處理單擊“訂閱”按鈕,方法getPublish正在處理單擊“發布”按鈕。問題如下:當我訂閱主題時,消息不要到達已訂閱該主題的客戶端。 怎么了?
如果我正確理解了您的問題,則您已訂閱主題“ sTopic”,但是當有人向主題“ sTopic”發布消息時,您沒有收到消息。
您確定Mqtt客戶端已成功連接到代理嗎? 進行訂閱呼叫之前,先使mqtt客戶端已連接。
if( mqttClient.isConnected()) {
mqttClient.subscribe(sTopic);
}
同樣也適用於發布。
if( mqttClient.isConnected()) {
mqttClient.publish(sTopic,message);
}
一旦這些調用結束,您應該在messageArrived回調方法中看到已發布的消息。
您需要將回調方法設置為mqttClient
clientCallback = new MqttCallback() {
@Override
public void connectionLost(Throwable cause) {
}
@Override
public void messageArrived(String topic, MqttMessage message) throws Exception {
}
@Override
public void deliveryComplete(IMqttDeliveryToken token) {
}
};
mqttClient.setCallback(clientCallback);
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