After having worked with various legacy codebases one discovers certain recurring traits and patterns. The topic of today is the Custom Exception Hierarchy encountered in Java legacy code. This phenomenon is rather Java-specific because of that language’s checked exceptions.
So what is a Custom Exception Hierarchy? It’s an exception hierarchy, with some strangely named exception at its root, present throughout the entire codebase and used everywhere. The author(s) of such hierarchy obviously felt that exceptions like IllegalStateException or IllegalArgumentException, or the like weren’t sufficient for the sophisticated needs of their application, so they came up with a better suited hierarchy of checked exceptions.