First, we will use the asynchronous API provided by the Paho Java client to create an MQTT asynchronous client that connects to the Mosquitto MQTT server. We will write a few lines of Java code to establish a secured connection, subscribe to a topic, and display the payload for the messages received in this topic. The synchronous API provided by the Paho Java client is simpler to use, but in most cases, we will want to use the non-blocking asynchronous API. Hence, we will focus on the asynchronous API.
In Chapter 2, Securing an MQTT Mosquitto Server , we have secured our Mosquitto server, and therefore, we will use the digital certificates we have created to authenticate the client. Most of the times, we will work with an MQTT server that uses TLS, and therefore, it is a good idea to learn how to establish a connection with TLS and TLS authentication. It is easier to establish an unsecured connection with an MQTT server, but it won't be the most...
