Top Most Jamon plugin for Grails: Part 1 of 4

JAMon is a popular, flexible, lightweight open source Java performance monitor. I won't cover all the features here, but in short JAMon can monitor performance, memory, number of users, basically any quantity you can access in Java.

To view the statistics JAMon provides a WAR file that you can deploy to your server along with your application. The war provides a set of JSP pages allowing you to view and export the data you are monitoring.

Another option is to incorporate the WAR into your application. It requires a little more work but you can enhance it to your hearts content.

Adding JAMon to Grails is really quite simple. What required some time was to experiment with the different methods JAMon can be inserted into your application. I prefer automation over hard-coded solutions.

Here are the tasks needed to get JAMon set up with an initial set of monitors:

1. Add jamon.jar to the application classpath
2. Use JAMon's datasource proxy to monitor SQL
   
3. Implement the JAMonServletFilter to monitor page hits
   
4. Leverage Spring AOP via Spring's JamonPerformanceMonitorInterceptor class to monitor services
5. Add a Spring filter to monitor Grails controllers.
   

Ideally it would be nice to separate this code in a way that JAMon could be applied to any Grails project. In fact, I found that to be the simplest approach! This solution just cries out for a Grails plugin.

I won't go into all the details regarding plugins. Good references are available here, here and here.

Fist download the JAMon distribution and unzip it.

Assuming you have a target application, let's assume you'll be creating your plugin in the same workspace (i.e. directory). Open a command prompt in that folder and type:

grails create-plugin jamon

If you've never created a plugin before you'll notice that Grails creates a typical Grails application with one additional file in the top directory: JamonGrailsPlugin.groovy.

This file is where we'll be doing most of the work.

To complete task #1 (add jamon.jar to the classpath), simple copy jamon.jar to jamon/lib. When an application installs the plugin, Grails will add jamon.jar to the classpath. That's all you need to do!

Next time I'll show how to implement the remaining tasks. Stay tuned.