Mqtt client with Java in Eclipse

I wrote a java code that receive messages from a Raspberry pi(as a sensor emulator) via MQTT client, so, for now it just printing the messages in the console of the Eclipse. I want to buffer that messages in a CSV file for example and then search for specific data in the CSV file(e.g. By the name of the sensor) and take that data and send it with MQTT to an SDN switch. Then I will run that code in a second Raspberry pi.