If you plan on the integration of a Java application (>= 1.5), the easiest approach lies in the utilization of BugTrap, a Java Sensor Module that deals with the most common requirements.
Proceed to BugTrap Java Sensor for a integration tutorial.
If there`s no suitable Sensor Module available for you application, you can choose to speak to the Aggregator directly using the offered external interfaces.
Proceed to the Naggregator J2EE Server project page for a description of the offered channels and communication strategies.