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In Spring MVC, the model works a container that contains the data of the application. Here, a data can be in any form such as objects, strings, information from the database, etc. It is required to place the Model interface in the controller part of the application.
Model defines a holder for model attributes and is primarily designed for adding attributes to the model. ModelMap is an extension of Model with the ability to store attributes in a map and chain method calls. ModelAndView is a holder for a model and a view; it allows to return both model and view in one return value.
Spring Boot, with Spring Boot WebMVC, make it easy to create MVC apps with very clear delineations and interactions. The Model represents formal underlying data constructs that the View uses to present the user with the look and feel of the application. A Controller is like a traffic cop.
Furthermore, there's also an addAttributes() method. Its purpose is to add values in the Model that'll be identified globally. That is, every request to every controller method will return a default value as a response.
The model presents a placeholder to hold the information you want to display on the view. It could be a string, which is in your above example, or it could be an object containing bunch of properties.
Example 1
If you have...
return new ModelAndView("welcomePage","WelcomeMessage","Welcome!");
... then in your jsp, to display the message, you will do:-
Hello Stranger! ${WelcomeMessage} // displays Hello Stranger! Welcome!
Example 2
If you have...
MyBean bean = new MyBean();
bean.setName("Mike!");
bean.setMessage("Meow!");
return new ModelAndView("welcomePage","model",bean);
... then in your jsp, you can do:-
Hello ${model.name}! {model.message} // displays Hello Mike! Meow!
new ModelAndView("welcomePage", "WelcomeMessage", message);
is shorthand for
ModelAndView mav = new ModelAndView();
mav.setViewName("welcomePage");
mav.addObject("WelcomeMessage", message);
Looking at the code above, you can see the view name is "welcomePage". Your ViewResolver (usually setup in .../WEB-INF/spring-servlet.xml) will translate this into a View. The last line of the code sets an attribute in your model (addObject("WelcomeMessage", message)). That's where the model comes into play.
It is all explained by the javadoc for the constructor. It is a convenience constructor that populates the model with one attribute / value pair.
So ...
new ModelAndView(view, name, value);
is equivalent to:
Map model = ...
model.put(name, value);
new ModelAndView(view, model);
Here in this case,
we are having 3 parameter's in the Method namely ModelandView.
According to this question, the first parameter is easily understood. It represents the View which will be displayed to the client.
The other two parameters are just like The Pointer and The Holder
Hence you can sum it up like this
ModelAndView(View, Pointer, Holder);
The Pointer just points the information in the The Holder
When the Controller binds the View with this information, then in the said process, you can use The Pointer in the JSP page to access the information stored in The Holder to display that respected information to the client.
Here is the visual depiction of the respected process.
return new ModelAndView("welcomePage", "WelcomeMessage", message);
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