Software Architect's Handbook

Refactoring legacy applications

When you begin working on a legacy application, you will want to refactor it in order to make it more maintainable. You may need to implement new features, fix defects, improve the design, increase quality, or optimize the application. In order to perform these types of task, the legacy system must be in a state where changes can easily be made and without much risk.

In the classic book Refactoring: Improving the Design of Existing Code, author Martin Fowler defines refactoring as …the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. Any refactoring that is performed should safely improve the code in some way, without ...