Advice on working with legacy code

Question

I need some advice on how to work with legacy code.

A while ago, I was given the task to add a few reports to a reporting app. written in Struts 1, back in 2005. No big

Answer 1

Rule #1: If it ain't broke, don't fix it.

Rule #2: When in doubt, reread rule #1.

Unfortunately, legacy code can very rarely be described as "it ain't broke." Therefor we must tweak the existing code to correct a newly found bug, tweak the existing code to modify behavior that was previously acceptable, or tweak the existing code to add new functionality.

My experience has taught me that any refactoring must be done in 'infinitesimally' small increments. If you must break rule #2, I suggest that you start your search with the inner-most nested loop or IF structure and expand outward until you find a clean, logical separation point and create a new function/method/subroutine that contains only the guts of that loop or structure. This won't make anything more efficient but it should give you a clearer view of the underlying logic and structure. Once you have several new, smaller functions/methods/subroutines you can refactor and consolidate those into something more manageable.

Rule #3: Ignore my previous paragraph and reread the first two rules.