Security Software

Hello Experts,

Please help me in develping knowledge to write custome event handlers. As per my understanding so fare, only way to customize user management in OIM is through event handlers which are according to my understanding from developer's guide are (small)peace java code.
Hope my understanding is right?
I can also see a well-defined process for creating it like creating jar >> creatling xml file >> creating an plugin.
Now my query is how do I develop JAVA code?
Is standard java coding practice not required (like creating projects in Eclipse) or coding will be simple enough so as it won't require much effort?
Is it like coding event handler is nothing but knowing OIM APIs and writing few lines of code?
How do I make a very deep understanding so that I am able to code for customization (or frankly speaking writing new event handlers)?

Please help me with your suggestion.

Thanks!