Doubt regarding parameter of type Model in methods of spring controller

[Monica Shiralkar]

I seen some Spring MVC controller code with parameter of the type Model. I have used spring controller but never used parameter of type Model. What is this parameter of type model in spring controller method for. Is it mandatory(I do not thing so as I have never used it and still run spring MVC code).

thanks

[Marcus Biel]

Monika,

dou you know the meaning of "mvc"? Model, View Controller. Look this up on google and read about it. In short, it's a design pattern that aims to separate different types of logic into their own components to simply coding as well as to improve code reuse.
The model is the "thing" that contains your data and your business logic. The model is also used as a means to store data that should later be displayed in the view (UI). So in the controller, store the data to be displayed into the view, which in spring mvc, as far as I remember
is just something like a simple map. In the view, you can then later access this model to display it - this is a way to decouple your controller from the view.

Does that help?

Cheers,

Marcus

[Monica Shiralkar]

Thanks.

I am aware of MVC and have worked on MVC frameworks like Struts,Spring MVC. I know that model is used to store data but I have known model in model view controller as a concept but not as a keyword or type. Even if we are not having a parameter of type model in spring controller method, still it functions as MVC as the concept of model is used there. My doubt is regarding model the keyword,the type rather than model the concept.

[Marcus Biel]

Sorry, you lost me, can't follow, please be more clear

[Monica Shiralkar]

I meant that I understand Model the concept (of MVC) but by doubt is regarding Model the keyword,the type (as used parameters of Spring controller method)

[Marcus Biel]

This is not just a "keyword". That is meant to be the model in mvc, well, at least a simplified version of it - It's just a map, as said before.

[Monica Shiralkar]

I will explain the doubt with an example.In the below code there is model of type ModelMap in the parameter of spring controller method but is is not used at all. Without it , the code still works fine.

@RequestMapping(value = "/getProducts.htm", method = RequestMethod.GET)
	public ModelAndView subCategoriesController(
			@RequestParam("categoryId") Long categoryId, ModelMap model) {
		 HomeManager homeManager = new HomeManager();
                 Set productSet= homeManager.getProducts(categoryId);
		 ModelAndView modelAndView = new ModelAndView("showproducts");
		 modelAndView.addObject("productSet",productSet);
                 return modelAndView;
	}

thanks

[Prasad Krishnegowda]

First, In your example, there is no need to include ModelMap attribute, if you are not using it.

ModelAndView as the name suggests includes both Model and the name of the view. ModelMap includes only model.
Controller allows to return both ModelAndView as single object using ModelAndView class.

Using ModelMap.addAtrribute we can add the data to model, and return the view name as String, like below.

@RequestMapping(value = "/getProducts.htm", method = RequestMethod.GET)
    public String subCategoriesController(
            @RequestParam("categoryId") Long categoryId, ModelMap model) {
                 HomeManager homeManager = new HomeManager();
                 Set productSet= homeManager.getProducts(categoryId);
                 model.addAttribute("productSet",productSet);
                 return "showproducts";
    }

[Monica Shiralkar]

thanks

Using ModelMap.addAtrribute we can add the data to model, and return the view name as String, like below

Yes, I had read this but I could not understand any difference which it makes if we do as above or by returning ModelandView object.

[Prasad Krishnegowda]

Returning String object and passing data through ModelMap is a newer approach in Spring, this approach will be familiar for people coming from struts background.
This said, it does not mean newer approach is better, hardly there are any difference.

[Monica Shiralkar]

thanks. In my code since I am not using the ModelMap at all and rather the modelandview parameter, let me try to remove the parameter and check.