[IOTDB-6296] Fix memory leak in MQTTService

[JackieTien97]

As we can see in the interface java doc: The receiver MUST release the payload of the message, either by calling super.onPublish, or by calling msg.getPayload.release() directly., otherwise the memory will leak.

we use MQTTClient in example/mqtt/src/main/java/org/apache/iotdb/mqtt, changes like:

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package org.apache.iotdb.mqtt;

import org.fusesource.mqtt.client.BlockingConnection;
import org.fusesource.mqtt.client.MQTT;
import org.fusesource.mqtt.client.QoS;

import java.util.Random;

public class MQTTClient {
  public static void main(String[] args) throws Exception {
    MQTT mqtt = new MQTT();
    mqtt.setHost("127.0.0.1", 1883);
    mqtt.setUserName("root");
    mqtt.setPassword("root");
    mqtt.setConnectAttemptsMax(3);
    mqtt.setReconnectDelay(10);

    BlockingConnection connection = mqtt.blockingConnection();
    connection.connect();

    Random random = new Random();
    for (int i = 0; i < 100000; i++) {
      String payload =
          String.format(
              "{\n"
                  + "\"device\":\"root.sg.d1\",\n"
                  + "\"timestamp\":%d,\n"
                  + "\"measurements\":[\"s1\"],\n"
                  + "\"values\":[%f]\n"
                  + "}",
              System.currentTimeMillis(), random.nextDouble());

      // publish a json object
      Thread.sleep(1);
      connection.publish("root.sg.d1.s1", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
    }
//    // publish a json array
//    sb.insert(0, "[");
//    sb.replace(sb.lastIndexOf(","), sb.length(), "]");
//    connection.publish("root.sg.d1.s1", sb.toString().getBytes(), QoS.AT_LEAST_ONCE, false);

    connection.disconnect();
  }
}

We can got the following result, for master branch we can see that the off heap will increase all the time, but this pr won't increase.

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud