Dynamic Command Class in Annotated Controller

Question

As of Spring MVC 3, AbstractCommandController is deprecated so you can no longer specify the command class in setCommandClass(). Instead you hard-code the command class in the parameter list of a request handler. For example,

@RequestMapping(method = RequestMethod.POST)
public void show(HttpServletRequest request, @ModelAttribute("employee") Employee employee)

My problem is that I'm developing a generic page that allows the user to edit a generic bean, so the command class isn't known until the run-time. If the variable beanClass holds the command class, with AbstractCommandController, you would simply do the following,

setCommandClass(beanClass)

Since I can't declare the command object as a method parameter, is there any way to have Spring bind request parameters to a generic bean in the body of the request handler?

Answer 1

Instantiation of the command object is the only place where Spring needs to know a command class. However, you can override it with @ModelAttribute-annotated method:

@RequestMapping(method = RequestMethod.POST) 
public void show(HttpServletRequest request, 
    @ModelAttribute("objectToShow") Object objectToShow) 
{
    ...
}

@ModelAttribute("objectToShow")
public Object createCommandObject() {
    return getCommandClass().newInstance();
}

By the way, Spring also works fine with the real generics:

public abstract class GenericController<T> {
    @RequestMapping("/edit")  
    public ModelAndView edit(@ModelAttribute("t") T t) { ... }
}

@Controller @RequestMapping("/foo")
public class FooController extends GenericController<Foo> { ... }