An insight into sonar plugin development

In the recent months, I've been involved in developing a language plugin for sonar that displays different metrics for a specified language. I am writing this post as there is not much content available for this topic even when sonar is a widely popular tool.

Below are tips to avoid some of the common pitfalls in developing sonar:

• Read the official documentation carefully, even when there isn't much of it.
• Download the sources of all the open source plugins and try looking their code for proper understanding into plugin development.
• Do read books available on the topic in addition to the blogs for proper understanding.
• Use maven, this is a real lifesaver and focus on TDD while coding - as you cannot hope to debug the process otherwise.

If you've followed these steps diligently,  you'd have a basic understanding on the innards of sonar plugin development.
In very brief words, a sonar plugin comprises of a java based program that performs the heavy duty work of loading/populating the code metrics and a ruby based UI (embedded ruby pages(erb)) that helps in displaying of this data, in a nice manner and also uses view helpers to create eye-catching widgets that display these data. There is another provision for a complete rails based application to be created in place of this, but that's a different idea altogether.

In my case, I needed to Populate the data from a database , so in a class implementing Sensor interface, following method was present

  public void analyse(Project project, SensorContext sensorContext)
Inside this method, I can use Project object to read from project properties,etc as inputs to my process and SensorContext object as output in the form of  measures;

sensorContext.saveMeasure(new Measure(MyMetricAnalysisClass.MetricName, Double.valueOf(metricVal)));

One of the nice features of working with erb templates in the UI for widgets is that you can use a lot of helper methods to create slick effects with your data. One such example is a piechart:
<%= piechart( 'Field1 = '+var1.to_s+'; Field2 = '+var2.to_s+';'  , { :size => "500x200"}) -%>

One caveat present while transferring the data from server to views is that only text data works well, the information about using data structures is sketchy at best so we are left with using the data delimimted with ';' (See the first argument in piechart helper method above). Surprisingly, other data cause widgets to fail with no descriptive error messages. For larger data, it is more intuitive to use a GWT page instead of a widget as the users can focus more on the details provided in the page as opposed to the concise totals present on the widgets.
Hope this post helps the users developing plugins on this platform something to get started with.