July 30, 2004

The last couple of days, I've managed to convert the MyUsers sample app from JSP to Velocity, and also to FreeMarker. Since this app uses SiteMesh, this was fairly easy thanks to its Velocity Decorator and FreeMarker Decorator support. Of course, Spring supports both technologies as well - ref: Spring+Velocity and Spring+FreeMarker. The real slick part of Spring's integration is that I didn't really need to change any code to support either templating engine. All I had to change was the XML in action-servlet.xml! Very cool!

In the process, I found out that FreeMarker is a bit more strict about the whole MVC thing. With Velocity and JSP, I can remove session variables using $request.session.removeAttribute("varName") and <c:remove var="varName"/>. I agree that doing this isn't very MVC-ish, but I was surprised to find that FreeMarker doesn't even allow this. It allows access to "request attributes", but not the "request" object itself. Of course, this makes it a pain to get the requested URL (request.getRequestURL()) as well.

Now I should explain why I have session variables that I'm removing in the view. The reason is because I save success messages in the session to survive redirects. It just seemed easier (at the time) to remove this variable after I rendered it in the view. Spring doesn't have any out-of-the-box support for success messages (like Struts ActionMessages), so it seems like a reasonable solution. To workaround the the FreeMarker limitation, I decided to add a MessageFilter that grabs messages from the session and puts them into the request. I also added "requestURL" as a request attribute - solving both of the issues I found with FreeMarker, and making my views more MVC-ish.

The one thing I really like about FreeMarker over Velocity is the ability to use JSP Tags in your template. To me, this is very powerful since displaytag and struts menu are my primary reasons for sticking with JSP. After implementing JSP 2.0, Velocity and FreeMarker - it's funny to see how the variable rendering syntax - ${...} - is very similar in all three. Even after implementing Velocity and FreeMarker, I think I'll stick with JSP (2.0) - it just seems a lot more powerful. No limitations if you will.

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