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 most significant difference is that "interceptors" are a part of the Struts 2 framework, and are only part of the request handling that is done by the Struts 2 framework. "Filters" on the other hand are a part of the Servlet Specifcation; in other words, they are part of the Servlet API. If you are using Struts 2, you should use interceptors for wrapping functionality around your Struts 2 actions. If you are trying to wrap functionality around requests coming to your webapp, but not being handled by Struts 2, then a filter might be more appropriate.

BTW, the entire Struts 2 Framework is deployed inside a filter configured in your web app, declared in your webapp's deployment descriptor ( web.xml ) like:

    <filter>         <filter-name>struts2</filter-name>         <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>     </filter>       <filter-mapping>         <filter-name>struts2</filter-name>         <url-pattern>/*</url-pattern>     </filter-mapping> 

This filter, which is configured to catch all requests URL patterns, is the entry point into the entire Struts 2 framework.

I hope that helps.