This is an example code from the HiveMQ Blog post "The missing piece between MQTT and a SQL database in a M2M landscape". This example project shows how a MQTT wildcard subscriber which stores all messages to a MySQL database could be implemented.
Why was Paho bundled with the code?
At the time of the writing, Paho was not yet mavenized. Since Maven is awesome (or at least one of the not-so-sucky build systems), we bundled Paho in a Maven file repository with this code.
Probably not, this is a proof of concept. However, this example project could get you started quickly for implementing a real world application. We recommend to use a sane Logging Library (like Logback) and upgrading to the latest Paho version. Probably Paho is already mavenized when you read this, make sure you check Maven central.
Important: Wildcard root subscribers are not the smartest way to store all MQTT messages into a database. See this link