Implementing a java agent to instrument code

With a system running 24/7, you have to make sure that it performs well at any time of the day. Several commercial solutions exist to monitor the performance of systems: NewRelic, GraphDat and many others. They allow to see for instance if the api call response time change week after week or after each release of the project. So the developers can easily spot where the bottlenecks are and fix them.

You can also use profilers such as JProfiler, YourKit, … to detect bottlenecks, memory leaks, thread leaks, …

Most of those tools works by using a java agent, a pluggable library that runs embedded in a JVM that intercepts the classloading process. By modifying the classloading process, they can dynamically change the classes instructions to perform method logging, performance measure, …

In this post we are going to describe how to implement a simple java agent to measure how frequently and how long some methods of your application take and publish the results to JMX and to Graphite.