Exception Handling Guideance in a JEE 5 Web App

Question

I’ve been surprised by how hard it is to find best practices for this on the web since it must be such a common problem.

App is based on Java 1.5 – JSF 1.2 with Faclets, Seam, JPA, Hibernate. Some Web Service calls. Some JMS.

I’m after general recommendations for Exception handling. There are roughly 3 approaches I’ve seen used but I’ve never been that sure which one is better. Assuming you can’t recover from an error do you: 1) Log the error when it occurs and re-throw it?
2) Log it when it occurs and throw some sort of generic exception?
3) Let it bubble up and then handle it in a generic exception handling servlet or similar.

I’ve tended to use option 2 on previous systems where the architecture has been fairly simple – an adaptor layer talking to various 3rd party systems throws and adaptor exception if it gets an error back and so on. We can display a nice clean message to the user on the screen and keep the details in a log. Here though the architecture is a lot more complex and I’m wondering how well it would work in practice. So I’m interested to know what you prefer and why.

Answer 1

Assuming you can’t recover from an error...

Assuming this error is not a functional error, I log the error and wrap the exception in an (custom) unchecked exception and let the framework/container handle it (so option 2). I like to do it his way because:

• I like to use container managed transactions and I want the container to do its job (i.e. rollback any transaction) so throwing a runtime exception is the way to go.
• It minimize the exception handling work.
• It make the reporting to the user easy to handle in a generic way.

If it's a functional error (i.e. an alternative flow in a use case), I log the error and wrap the exception in a (custom) checked exception because I want the caller to handle it specifically as the problem is part of the use case.

In both case, I use a root exception for each hierarchy, namely TechnicalException and FunctionalException.