Object Counter

Overview

Using AspectJ to experiment with counting objects created within a JVM.

To see it in action:

1. Clone the project within your chosen directory, from the command line

    git clone https://github.com/elegantmush/objectcounter.git
   

2. Change to the project directory

    cd objectcounter
   

3. Execute the ObjectCounterIT integration test

    mvn -Dit.test=ObjectCounterIT clean verify
   

What's going on?

The code to count created objects comprises an aspect, com.elegantmush.objectcounter.aspect.CounterAspect and a singleton enum, com.elegantmush.objectcounter.ObjectRegistry. The aspect captures all initial calls to a constructor - i.e. it ignores implicit calls to super() and constructors called via this() chaining. The enum uses a java.util.concurrent.ConcurrentMap<String, Integer> to store fully qualified classnames and associated counts.

What's next?

• JMX view on the object count
• Spring librari-fication, so that it can be dropped into an existing project seamlessly and without effort on the project owner's part.

Why?

Well.. the object counting caper may not be of much use, but the principles of weaving into existing code, being able to use JMX to monitor the effects of the woven-in functionality, and to be able to provide drop-in Spring libraries that enable auxillary functionality to existing projects have potentially far-reaching benefits.

We can gain an understanding of these principles and generalise how to practically effect them by using dummy example functionality such as object counting.