HiveMQ MQTT Client Java: Is there a way to check if a topic matches a subscription?

Is there a built in way to check with hivemq-mqtt-client if a specific topic matches another topic in advance?

For instance, a message published with topic:

publishedTopic= "sensors/sensor1";

A client that subscribes:

subscribedTopic = "sensors/#";

Is there something like

publishedTopic.matches(subscribedTopic)

The exact situation:

I run a broker in my house, several devices publish values with different topics. Some like sensor/humi[45], some like sensor/data[JSON Payload]. For my personal use I run an application using Java HiveQM MQTT clients. One client is subscribed to relevant topics using mosquitto on raspberryPi. The other client is publishing selected data to a public accessible broker. Receiving a new message will not only process all data in the way I process it but also trigger a publishing the received message to the public broker.

Yes, I can

if(topic.equals("sensor/xxx")) {
//publish to public broker here
}

But doing some like subscribing to "sensor/#", from my internal broker, and "forwarding" something like "sensor/+", and letting a library doing the job of determining if a certain message that is received with "sensors/#", will be republished to the public broker, limited to "sensors/+" is what I am looking for.

Is the logic inside HiveMQ mqtt-client library, which obviously filters in that exact way, when I subscribe to "sensors/#", accessible for the library user?

Solution

One way to achieve what you want is to use a particular callback for the topics you want to forward.

Using HiveMQ library you can define a callback to consume the received message per subscribe or globally matching a given filter.

In your case you could use a per subscribe consumer for the topics which should be handled in a special way:

client.subscribeWith()
        .topicFilter("sensors/sensor1")
        .qos(<qos>)
        .callback(<callback for topics to be forwarded>)
        .send();

Followed by a global filter matching all topics which are not yet consumed:

client.publishes(MqttGlobalPublishFilter.REMAINING, <callback for other topics>))

(and the subscription to sensors/# of course)

This way only sensors/sensor1 will be consumed in your first callback and sensors/sensor2, sensors/sensor3 (and so on) are consumed by the other callback