Implementing MQTT for Clients and Server: Eclipse has a project called “paho” that provides libraries for us to make use of and make our development of Clients and Servers that need MQTT easy. We need to just write the logic around MQTT and use the APIs that implement the actual MQTT protocol methods. this makes it easy for IOT developers to concentrate on the IOT logic vs the MQTT protocol workings.
The word pāho (verb) means to broadcast, make widely known, announce, disseminate, transmit (via the Maori dictionary). The Paho project has been created to provide scalable open-source implementations of open and standard messaging protocols aimed at new, existing, and emerging applications for Machine-to-Machine (M2M) and Internet of Things (IoT).
I have explained in udemy on how to write a most basic 100 line app on Android using Java. Please take a look at the udemy course and at the end of the 30 min tutorial, you will be able to write your own MQTT Client, that you can test with any of the well known freely available MQTT Servers on the cloud, e.g. iot.eclipse.org. Please use ASEEM_MQTT coupon to avail a discount when you checkout the course.
You can also see the fully developed app in Google Play - https://play.google.com/store/apps/details?id=com.asethi.mqttapp , and the complete source code for the Android App in github https://github.com/aseemsethi/iot . This Android App basically builds on the udemy course, and provides for more options in User Interface. Other than that, it’s core logic is the same as the basic app in the udemy course.