Spring MVC Details

1. What is a Model Attribute?

• Definition: A model attribute is a server-side key-value pair (String, Object).

• Purpose: To share the results of business logic from the handler (Controller) to the View layer.

• Who Creates: The request-handling Controller (handler), supplied by the programmer.

• Who Sends to Whom: Handler sends it to the DispatcherServlet (D.S).

• Process:

  • After the DispatcherServlet gets the actual view name from the ViewResolver (V.R):
    • If model attributes exist: D.S saves them under Request scope and forwards the request to the View layer.
    • If no model attributes: D.S forwards the request to the View layer.

• Accessing Model Attributes in JSP:

  ${requestScope.attrName}
  
  

1.1 Ways to Add Model Attributes

Via org.springframework.web.servlet.ModelAndView

• Definition: ModelAndView is a class that holds model attributes and the logical view name.

• Constructor:

  ModelAndView(String forwardViewName, String modelAttrName, Object modelAttrVal)
  
  

• Valid Return Types for Request Handling Method:

  • String (logical view name)
  • ModelAndView

1.2 Simpler Way to Send Model Attributes from Handler to DispatcherServlet

• Using: org.springframework.ui.Model interface.

• Definition: Represents a holder (Map) of model attributes.

• How to Add Model Attributes:

  public Model addAttribute(String modelAttrName, Object modelAttrVal)
  
  

• Adding Multiple Model Attributes: Use method chaining.

• Who Supplies the Empty Model Map: Spring Container (SC) via Dependency Injection (DI).