Filters vs Interceptors in Struts 2

Question

What's the difference, really, between filters and interceptors? I realize that interceptors fire before and after an action, recursively, and filters can be configured to fire on actions and on certain url patterns. But how do you know when to use each one?

In the book I'm reading on Struts 2, it seems that interceptors are being pushed and I even followed a tutorial to write an Authentication Interceptor to make sure a user is logged in. However, if the user tries to access a URL that doesn't have an action associated with it, the interceptor doesn't catch it, which means I'd have to associate an action with every jsp that I want to be secure. That doesn't seem right.

I can make an Authentication Filter that handles URLs so that I don't have to do that, but then, what's the point of interceptors?

Answer 1

the interceptor stack fires on every request.
filters only apply to the urls for which they are defined.

edit -- you use one or the other depending on need. Lets say you need to verify a cookie is present for every request. User an interceptor. Lets say that you need to pop up an external app on some requests (driven by a url), use a filter.

I think interceptors are the more commonly used tool...

why would you have a url with no associated action?