Since starting developing some code generation plugins (toString() generator and Java Util Logger Generator) using/for the NetBeans 6.1Beta I have learnt a lot and the more I worked on it I kept asking myself how could I make it easier. Once both the plugins took rudimentary form I learnt and discovered that patterns could make this task whole lot easier for me. So I started re-implementing the Logger generator (if you are interested in getting the resources please check the logger blog) plugin.
Now I wanted to implement that the plugin will search for System.out.print(ln) and out.print(ln) if static import exists. In doing so I had to walk the PARSED tree of a Java Source file. Just to give me a flavour that I am implementing something cool I called it JavaSourceTreeParser. Basically what it does is breaks down each every Java Statement to a form which can not be further decomposed. In the initial version the conversion was done in the parser it self (Revision 21). Then it felt that I could easily use Observer pattern for it and after implementing it (Revision 31) I saw that I am right and I achieved something which every code generator can use. (As I use GIT SCM I usually work offline and make bunch of commits together so dont worry how I make multiple commits at a go :)).
Once implementing it I found that for performance improvement and communication between various listeners I felt the need of session for state information sharing and then I decided to use Composite pattern for the purpose. and it also worked like a charm and as a result improving the overall performance of the plugins. The following diagram might give an idea how to use it using the API I designed.
What I implemented in the listener simply that the listener will get notified whenever the parser come across a particular type of tree, for System.out.println it would be MethodInvocationTree (Kind.METHOD_INVOCATION), and the listener according to its implementation will handle the Tree; in my case I replaced the method invocation with a logger invocation. In case where I inserted a Log method at the beginning of every method body I listened to Kind.METHOD. Now I am implementing Log insertion for Throw, Return and End of Method block. In process I will also add parsing life cycle listener to the API so that modification to the class is done only once when the parsing is completed. I hope this API helps users interested in code generation. I am very interested to learn what users think about it.