Spring MVC vs Struts Part 2

This Part 2 of my experience switching from Struts to Spring MVC. Part 1 is here.

Now, before I get attacked by a Spring expert I am not claiming that this as a "best practices" post. I'm just describing my experience with Spring MVC and the solution I came up with. I would truly welcome a Spring veteran to come along and explain the right way to do it.

What I wanted was to retrieve certain information from the model and inject it into the view whether one was coming to the controller from the form submission or from any other source, like a link. At first I tried using the formBackingObject since it is always called but since one doesn't have access to the ModelAndView there that doesn't work well. I tried using handleRequest which is also always called but since I was therefore overriding the method from a superclass, which calls onSubmit, I was masking that functionality and causing my onSubmit to be uncalled. I then tried using showForm, which is called to display the form. This ended up being my final, relatively satisfying, solution. It did leave one problem. I wanted to return to the same form after submission but that proved tricky to do from onSubmit. My solution was to call showForm from onSubmit and then return the ModelAndView returned by showForm.

This has been working pretty well, although not entirely aesthetically satisfying. I wish it was simpler but as with many things, once you figure it out, it's not too bad. If you doubt it's complex check out the workflow in the Javadoc. One has to consider both the workflow in the class and all it's superclasses. On the plus side this give one a great deal of control over how a request is handled.

But when my headache reaches a certain threshold, I long for Struts.

Note: I will post the actual source soon, in a more detailed description of this project.

Spring MVC vs Struts

I mentioned a few posts ago that I recently switched from Struts 2 to Spring MVC as my web development platform for a current project. I also mentioned that so far I don't regret my decision although I have some reservations. What I like about Spring MVC is that 1. it's more closely integrated with Spring, and Spring is most assuredly a worthy invention and 2. it does have in certain respects more flexibility than Struts. I'll probably have more to say on those strengths later but for now the point is that that's also Spring MVCs weakness. With flexibility often comes complexity and the Spring MVC controller model is definitely complex relative to Struts'.

Struts has a very tight and simple coupling between the view and the controller. In Webwork (the predecessor to Struts 2) it was extremely simple. You registered your controllers in xwork.xml and referenced them in the actions of your forms and your controller's execute would be automatically called by Webwork on each form submit. A get request directly from a URL is handled in exactly the same way. In Struts 2 it's similar, although a little more flexible. In the struts.xml file one can configure specific methods of the controller to be called, so you aren't just stuck with execute. That was a nice addition.

In Spring MVC it's more complex. First of all Spring MVC mirrors the HTTPServlet doGet/doPost methods more closely as opposed to Struts higher level of abstraction. But Spring adds more methods to handle different cases like onSubmit for form sumission, showForm to display the view and formBackingObject to link the model to the view. These are all chained together depending on the way the controller is entered, say a URL get vs. a form post. Contrast this with the simple description for Struts I gave above. Just one method called, configurable in the struts.xml, no matter how the form is called.

Where I ran into trouble was to be able to have identical things happen whether a user came to the controller via a link or a form submission. I want to check if the user is logged in and I want to retrieve certain information from the model whether this is the initial display of the view or a form submission. The problem is, which methods to use? There are so many to choose from and some don't get called in certain circumstances. Do I use doPost, handleRequest, formBackingObject, showForm or some combination thereof?

Since this post is getting a little too long I think my solution is going to have to be in a "to be continued".

So, stay tuned.