@Controller annotation query

[Abhay Agarwal]

Hi

I am new to Spring 3.0 and was just running one of the sample code of Spring MVC 3.0.

In sample code , i am using @Controller annotations.As we know that Controller can be Abstract Controller, SimpleFormController, MultiFormController etc.
When i placed @Controller above my POJO class definition (used for MVC operation), how Spring Annotation Handlers is deducing that this POJO class is to be treated as SimpleFormController class? not as MultiFormController class?

@Controller
@RequestMapping("/userRegistration.htm")
@SessionAttributes("user")
public class FirstController {
	
	private UserService userService;
	
	
	@Autowired
	public void setUserService(UserService userService) {
		this.userService = userService;
	}


	@RequestMapping(method = RequestMethod.GET)
	public String showForm(ModelMap model)
	{
		User user = new User();
		model.addAttribute(user);
		return "userForm";
	}
	
	
	@RequestMapping(method = RequestMethod.POST)
	public String completeForm(@ModelAttribute("user") User u)
	{
		userService.add(u);
		return "userSuccess";
	}
	
	
	
}

[David Newton]

Do you mean MultiActionController?

[Abhay Agarwal]

Yes

[Mark Secrist]

NOTE: I changed this first part because I misread the original question

The way you've annotated your controller, it's configured like a SimpleFormController (i.e. one path with separate GET & POST handler methods). The thing that controller annotations do is blur the lines between the old ideas of form controller and multiaction controller. Basically, you can do either or both in the same controller now. Anything you could do with the old SimpleFormController, you can pretty much do with annotations.

If you watch the startup and you've got full logging turned on, you'll see that the annotation handler deduces a lot from the annotations you've got. That's the convention over configuaration showing up. On the other hand, a multi-action controller would look more like the following (using your example) and takes advantage of more explicit path definitions. Notice how it's possible to blend both SimpleFormController behavior with MultiActionController behavior.

 @Controller  
//Note no @RequestMapping, although you could have a parent path like /admin or something here   
@SessionAttributes("user")   
public class FirstController {   
       
    private UserService userService;   
       
       
    @Autowired  
    public void setUserService(UserService userService) {   
        this.userService = userService;   
    }   
  
    // Note you don't need the .htm suffix as the mapping will allow /userRegistration.*
    // It will respond to /userRegistration.do, /userRegistration.htm, etc
    @RequestMapping(value="/userRegistration" method= RequestMethod.GET)   
    public String showForm(ModelMap model)   
    {   
        User user = new User();   
        model.addAttribute(user);   
        return "userForm";   
    }   
       
       
    @RequestMapping(value="/userRegistration" method= RequestMethod.POST)   
    public String completeForm(@ModelAttribute("user") User u)   
    {   
        userService.add(u);   
        return "userSuccess";   
    }   

   // Typical get method call with parameter (ex: http://someserver:8080/webApp/productList?productCat=bearings)
  // Note all the above parameters can be used here
   @RequestMapping(value="/productList" method=RequestMethod.GET)
    public String otherMethod(@RequestParam("productCat") String productCategory, Model model) {
      ... // Use the productCategory parameter to do some sort of filtered search & set result list in model
      mode.addAttribute("someModel", modelObj);
      return "viewName";
   }

   // This gets even cooler!!
   // Using URI Template
   // Note all the above parameters can be used here
  @RequestMapping(value="/getProduct/{productId}" method=RequestMethod.GET)
    public String getProduct(@PathVariable long productId, Model model) {
     // Now I can use the productId passed in to look up a product & set in the model
      ... //do some work
      mode.addAttribute("someModel", modelObj);
      return "productViewName";
   }
       
       
       
}  

[David Newton]

Are there any reasons to use one over the other? I also thought they looked really close to each other at a high level once you could add the annotations, but I don't know enough to understand any real differences, either.

[Mark Secrist]

David Newton wrote:Are there any reasons to use one over the other? I also thought they looked really close to each other at a high level once you could add the annotations, but I don't know enough to understand any real differences, either.

Are you asking annoteded vs. extension of SimpleFormController & MulitActionController?

[David Newton]

Mmm, more or less. It just seems like with the annotations there's no real need to think about the distinction--but want to know if that's actually true, or if there's other reasons someone might choose one over the other.

[Mark Secrist]

Yes, it's true that with annotations the distinction becomes blurred. In the past, you had to think about it more explicitly because the behavior was built into the class you extended and you could only extend from one. With annotations, you could make one controller class handle both form processing and other miscellaneous calls that might be considered multi-action. In fact, it's possible to have one controller handle muliple forms if you set it up right - but probably not a good idea.