Recommendations for migrating a legacy web app to a modern framework

Question

I am currently doing some work for a company that runs a legacy web app built on Java Servlets (the system pre-dates JSP's, although they now use them when building new pages). The code base is a big jumbled mess as its around 10 years of building on top of an out of date framework. They have very little consistency in the code base(the app has been developed by various people over the years, most of which no longer work here), no concept of DRY (every page is basically created from scratch) a lot of unreadable / cryptic code and just in general a very inconsistent infrastructure.

As I have been working here I have been adding in modern features / trying to clean up the code base a little bit. I added some jQuery to where I was exposed, introduced a bit of security with input validations, cleaned up some of the modules to employ unobtrusive JavaScript principles etc. My work here is on new modules so I am not exposed to a lot of the old logic. I have tried to introduce best practices to all my work under their current infrastructure but I am forced to call a lot of their old code to make my stuff consistent.

They have reached a point where they are now considering a massive update to the system. They want to improve the maintainability of the code base and attempt to move to some sort of modern framework / MVC type application. A lot of the system predates XHTML with inline stylistic markup, javascript:function() calls, no unit testing, predates Hibernate, etc. There is a mix of out.println html generation and calling jsp's from within the Servlet.

Some apps they have been looking at include Wicket, Struts, Tapestry and possibly Grails. The problem is, the move to any of these may require a huge rewrite of a system that is already in use and they cannot afford to start over.

My question is: What would be the best way to migrate a legacy code base such as this to a more modern framework while keeping the existing business logic (no sense in rewriting stuff that has been tested and works).

Some of the ideas being thought of include:

• write an in house templating system that would work with their current infrastructure (generate pages in a consistent way)

• port code to a framework such as tapestry (reusing a lot of their old code)

• rewrite system from scratch using a modern framework but copying over logic from old system (if possible)

• keep the old system as is and just update the front end pages to give it a more modern look (might be best given time/money etc.)

what is the best way to update legacy Java Servlet code to a modern framework (using modern practices for easy maintenance, unit testing, DRY) while keeping the logic intact?

any insight is welcome.

Answer 1

Refactor the hell out of it, working toward a consistent style of design, as a preliminary to porting it over to the framework closest in spirit to whatever that style ends up being.

By "refactor" I mean - introduce tests in strategic locations, unit as well as functional, and work like mad to reduce duplication, leaning on these tests.