Spring MVC Concepts

1. What is a Model Attribute?

• It's the attribute (server-side entry = key-value pair: String, Object)
• Purpose: To share the results of Business Logic (B.L) from Handler ---> View layer
• Who creates: Request handling Controller (handler) -- programmer-supplied
• Who sends it to whom: Handler ---> DispatcherServlet (D.S)
• Process:
  • After D.S gets actual view name from ViewResolver (V.R):
    • D.S checks: Are there any model attributes?
      • Yes: D.S saves model attributes under Request scope & then forwards the client to view layer.
      • No: D.S forwards the client to view layer.
• How to access these model attributes from JSP?
  • ${requestScope.attrName}

What are different ways for handler to add model attributes?

1.1 Via org.springframework.web.servlet.ModelAndView?

• Definition: It's a class representing a holder for model attributes + logical view name

• Constructor:

  ModelAndView(String forwardViewName, String modelAttrName, Object modelAttrVal)
  
  

• What will be the valid return type of request handling method?

  • String OR ModelAndView: ModelAndView

1.2 Any Simpler way to send model attributes from Handler (Controller) --> D.S?

• Use: org.springframework.ui.Model interface

• Definition: It represents holder (Map) of model attributes

• How to add model attributes?

  public Model addAttribute(String modelAttrName, Object modelAttrVal)
  
  

• Example: How to add multiple model attributes?

  • Method chaining

• Who will supply empty Model map (as the dependency)?

  • Spring Container (SC)