The Path to Zen

Spring Controllers with Prototype Scope

Most of the time, we configure the controllers in our Spring MVC application to be singletons, because of the their stateless nature. However, being configured as normal Spring beans, Spring controllers can also be declared with the prototype scope. Sometimes, it can actually be quite a useful feature. For instance, in a controller that descends from SimpleFormController, let’s say the formBackingObject() method needs to load an object from the DB that is necessary to instantiate the actual form object, and that same object also will also be used during onSubmit and/or referenceData(). Otherthan either reloading the object later, or resorting to storing the object in the request or even the session, a more convenient, less prone to name space clashing, and arguably more OO approach would be making it an instance variable, and making the controller a prototype bean.

Unlike a singleton controller, a prototype scope controller must have its bean name added to the ‘mappings’ property of the SimpleUrlHandlerMapping bean, instead of the ‘urlMap’ property, which requires an actual bean reference. The small price here is that, since the bean name is textually added to the mapping, there won’t be any XML validation against it. (In fact, I don’t think Spring IDE would catch an invalid bean name here either.)