如何使用 Eclipse Paho 使用 Java MQTT 客户端仅发布一条消息答案

【问题标题】：How to publish only one message using a Java MQTT client using Eclipse Paho如何使用 Eclipse Paho 使用 Java MQTT 客户端仅发布一条消息
【发布时间】：2016-11-04 22:02:58
【问题描述】：

我正在为我的大学期末作业做一个项目。我想做一个使用 MQTT 协议与我的树莓派通信的 android 应用程序。为此，我正在使用蚊子代理，但是当我使用 Eclipse Paho 使用 Java MQTT 客户端在代理中发布消息时，我的应用程序发布了 5 次相同的消息，我不知道问题是否出在我的班级发布消息，或者我的类 on_create() 的android。

我的代码如下：

public class MainActivity extends AppCompatActivity implements    View.OnClickListener {
EditText distanceCondition;
EditText timeCondition;
EditText countCondition;

String distance;
String time;
String count;
String topic;

int notificationID = 1;
int functionality;
int ok = 1;

public void mqttconnect(final String topic, final String message){

    final MqttAndroidClient mqttAndroidClient = new MqttAndroidClient(this.getApplicationContext(), "tcp://192.168.1.36", "androidSampleClient");
    mqttAndroidClient.setCallback(new MqttCallback() {                                      //iot.eclipse.org:1883
        @Override
        public void connectionLost(Throwable cause) {
            System.out.println("Connection was lost!");

        }

        @Override
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            System.out.println("Message Arrived!: " + topic + ": " + new String(message.getPayload()));
            //displayNotification("DETECT MOVEMENT! visit LCESS app now.");
            JSONObject inf = new JSONObject(Arrays.toString(message.getPayload()));
            try {
                if (inf.optString("Functionality").equals(6)) {
                    if (inf.optString("ok").equals(1)) {
                        displayNotification("DETECT MOVEMENT! visit LCESS app now.");
                    }
                }
                if (inf.optString("Functionality").equals(7)) {
                    if (inf.optString("ok").equals(1)) {
                        displayNotification("DETECT MOVEMENT IN" + inf.optString("Distance") + " CM! visit LCESS app now.");
                    }
                }
                if (inf.optString("Functionality").equals(8)) {
                    if (inf.optString("ok").equals(1)) {
                        displayNotification("DETECT MOVEMENT IN" + inf.optString("Time") + " HOURS! visit LCESS app now.");
                    }
                }
                if (inf.optString("Functionality").equals(9)) {
                    if (inf.optString("ok").equals(1)) {
                        displayNotification("DETECT MOVEMENT IN" + inf.optString("Distance") + " CM and in " + inf.optString("Time") + " HOURS! visit LCESS app now.");
                    }
                }
                if (inf.optString("Functionality").equals(10)) {
                    if (inf.optString("ok").equals(1)) {
                        displayNotification("DETECT " + inf.optString("Count") + " OBJECTS/PERSONS! visit LCESS app now.");
                    }
                }
            }
            catch (Exception functionality){

            }

        }

        @Override
        public void deliveryComplete(IMqttDeliveryToken token) {
            System.out.println("Delivery Complete!");
        }
    });

    try {
        mqttAndroidClient.connect(null, new IMqttActionListener() {
            @Override
            public void onSuccess(IMqttToken asyncActionToken) {
                System.out.println("Connection Success!");
                try {
                    System.out.println("Subscribing to: "+ topic);
                    mqttAndroidClient.subscribe(topic, 0);
                    System.out.println("Subscribed to: "+ topic);
                    System.out.println("Publishing message..");
                    mqttAndroidClient.publish(topic, new MqttMessage(message.getBytes()));
                } catch (MqttException ex) {
                }
            }

            @Override
            public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                System.out.println("Connection Failure!");
            }
        });
    } catch (MqttException ex) {

    }


}

public JSONObject sendJSONmessage() {
    topic = "Mesurement";
    distance = distanceCondition.getText().toString();
    time = timeCondition.getText().toString();
    count = countCondition.getText().toString();

    JSONObject post_dict = new JSONObject();
    try {
        post_dict.put("Topic", topic);
        post_dict.put("ok" ,ok);
        post_dict.put("Functionality", functionality);
        post_dict.put("Distance", distance);
        post_dict.put("Time", time);
        post_dict.put("Count", count);

    } catch (JSONException e) {
        e.printStackTrace();
    }
    if (post_dict.length() > 0) {
        System.out.println(post_dict);
    }
    return post_dict;
}

protected void displayNotification(CharSequence contentText){
    Intent i = new Intent(this, NotificationActivity.class);
    i.putExtra("notificationID", notificationID);

    PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i, 0);
    NotificationManager nm = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
    CharSequence ticker ="Notification in LCESS";
    CharSequence contentTitle = "LCESS";

    Notification noti = new NotificationCompat.Builder(this)
            .setContentIntent(pendingIntent)
            .setTicker(ticker)
            .setContentTitle(contentTitle)
            .setContentText(contentText)
            .setSmallIcon(R.drawable.lcess)
            .addAction(R.drawable.lcess, ticker, pendingIntent)
            .setVibrate(new long[] {100, 250, 100, 500})
            .build();
    nm.notify(notificationID, noti);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    distanceCondition = (EditText) findViewById(R.id.edit_detectDistanceCondition);
    timeCondition = (EditText) findViewById(R.id.edit_detectTimeCondition);
    countCondition = (EditText) findViewById(R.id.edit_countDetects);

    Button button_detectDistance = (Button) findViewById(R.id.button_detectDistance);
    Button button_detectDistanceCondition = (Button) findViewById(R.id.button_detectDistanceCondition);
    Button button_detectTimeCondition = (Button) findViewById(R.id.button_detectTimeCondition);
    Button button_detectIfAllCondition = (Button) findViewById(R.id.button_detectIfAllCondition);
    Button button_count = (Button) findViewById(R.id.button_count);
    assert button_detectDistance != null;
    /*button_detectDistance.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            functionality = 1;
            mqttconnect("Device1/Detect", sendJSONmessage().toString());
        }
    });*/
    button_detectDistance.setOnClickListener(this);
    assert button_detectDistanceCondition != null;
    button_detectDistanceCondition.setOnClickListener(this);
    assert button_detectTimeCondition != null;
    button_detectTimeCondition.setOnClickListener(this);
    assert button_detectIfAllCondition != null;
    button_detectIfAllCondition.setOnClickListener(this);
    assert button_count != null;
    button_count.setOnClickListener(this);
}

public void onClick(View v){
    if (R.id.button_detectDistance==v.getId()){
        functionality = 1;
        mqttconnect("Mesurement", sendJSONmessage().toString());
    }
    else if (R.id.button_detectDistanceCondition==v.getId()){
        functionality = 2;
        mqttconnect(sendJSONmessage().optString(topic), sendJSONmessage().toString());
    }
    else if (R.id.button_detectTimeCondition==v.getId()){
        functionality = 3;
        mqttconnect(sendJSONmessage().optString(topic), sendJSONmessage().toString());
    }
    else if (R.id.button_detectIfAllCondition==v.getId()){
        functionality = 4;
        mqttconnect("Device1/Detect1", sendJSONmessage().toString());
    }
    else if (R.id.button_count==v.getId()){
        functionality = 5;
        mqttconnect("Device1/Detect1", sendJSONmessage().toString());
    }
}

}

首先，我创建了 Mqtt 类来发布和订阅主题，之后，该类以 JSON 格式发布我需要的消息。

下一个类我用它来显示一个通知。最后是 onCreate() 和 onClick 类，我在其中声明了我的按钮、edittext...以及我放置发布消息的条件的地方。更具体地说，当按下按钮时，我会在 JSON 格式的主题中发布消息。

应用程序运行良好。但问题是：如何在代理中只发布一条消息？

在下图中，您可以看到当我按下按钮时如何发布 5 消息。 In red you can see the message published 5 or 6 times

【问题讨论】：

标签： java android mqtt mosquitto paho

【解决方案1】：

我解决了这个问题。在这种情况下，我如何构建一个与代理连接的函数，每次单击某个按钮时，我都会再次发布并订阅该主题。只有我必须订阅一次。解决方案是连接到中断并订阅主题，仅一次，因此我们实现相同的代码，但在 onCreate() 方法中。

【讨论】：

【解决方案2】：

String msg = "{\"uuid\":\"12345678\"}";
MqttMessage m = new MqttMessage();
m.setPayload(msg.getBytes());
m.setQos(2);
m.setRetained(false);
mqttAndroidClient.publish(topic, m);

【讨论】：