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Spring Web MVC

Spring's web framework is built on the Servlet API and deployed on its own embedded Servlet container. Centered around its Dispatcher Servlet, Spring MVC handles much of the complexity of the request-response cycle.

MVC Design Pattern

  • Model: The data being passed, rendered, and manipulated
  • View: What will be displayed, usually as html
  • Controller: Handles logic, routing

Spring MVC Request-Response Flow

  1. Request sent to DispatcherServlet
  2. DispatcherServlet calls HandlerMapping for help with request URI
  3. HandlerMapping looks up the handler for the URI, a registered Controller which is returned to the DispatcherServlet and called
  4. Controller is the entry-point for an event in and out of the rest of the program
  5. Controller returns a View name & Model to the DispatcherServlet
  6. DispatcherServlet consults ViewResolver to interpret View name as a template file and weave the Model into the response body
  7. Response sent to client

DispatcherServlet

Spring MVC's front controller has its own WebApplicationContext, allowing it to handle more bean scopes than singleton and prototype. It manages Controllers, HandlerMapping, ViewResolver, and all other components.

HandlerMapping

While configurable using RequestMappingHandlerMapping objects, it can be simply enabled using a <mvc:@annotation-driven/> element tag in configuration, allowing for component scanning to automatically register all @Controller and similar beans along with their mappings. It is responsible for routing requests to specific methods within these controllers.

Controllers

A @Controller stereotype annotation registers a class as a library of methods mapped to URI paths to handle requests. Several related annotations help to further specify these requests and their expected responses.

  • @RequestMapping specifies the URI with attributes like value for the path and method for the HTTP verb, and can be defined at the class or method level.
  • @GetMapping is a shorthand form of a @RequestMapping with GET assumed as its method. Also has siblings in @PostMapping and similar annotations.
  • @RequestParam can be used on method parameters to bind form or query attributes to arguments.
  • @PathVariable can be used on method parameters to bind URI path variables to arguments.
  • @ResponseBody tags a method (or all methods of a class) to write their return objects directly to the response body, skipping the ViewResolver entirely.

ViewResolver

ViewResolvers handle server-side view resolution for static HTML/CSS/JS files, or rendering for dynamic templates like JSPs or Thymeleaf files.