Controller (Spring Framework 3.2.1.RELEASE API)
Date: 2013-01-24

org.springframework.web.servlet.mvc

## Interface Controller

- All Known Implementing Classes:
    AbstractCommandController, AbstractController, AbstractFormController, AbstractUrlViewController, AbstractWizardFormController, BaseCommandController, CancellableFormController, MultiActionController, ParameterizableViewController, ServletForwardingController, ServletWrappingController, SimpleFormController, UrlFilenameViewController

      public interface Controller

  Base Controller interface, representing a component that receives `HttpServletRequest` and `HttpServletResponse` instances just like a `HttpServlet` but is able to participate in an MVC workflow. Controllers are comparable to the notion of a Struts `Action`.

  Any implementation of the Controller interface should be a reusable, thread-safe class, capable of handling multiple HTTP requests throughout the lifecycle of an application. To be able to configure a Controller easily, Controller implementations are encouraged to be (and usually are) JavaBeans.

  Workflow

  After a DispatcherServlet has received a request and has done its work to resolve locales, themes and suchlike, it then tries to resolve a Controller, using a `HandlerMapping`. When a Controller has been found to handle the request, the `handleRequest` method of the located Controller will be invoked; the located Controller is then responsible for handling the actual request and - if applicable - returning an appropriate `ModelAndView`. So actually, this method is the main entrypoint for the `DispatcherServlet` which delegates requests to controllers.

  So basically any direct implementation of the Controller interface just handles HttpServletRequests and should return a ModelAndView, to be further interpreted by the DispatcherServlet. Any additional functionality such as optional validation, form handling, etc should be obtained through extending one of the abstract controller classes mentioned above.

  Notes on design and testing

  The Controller interface is explicitly designed to operate on HttpServletRequest and HttpServletResponse objects, just like an HttpServlet. It does not aim to decouple itself from the Servlet API, in contrast to, for example, WebWork, JSF or Tapestry. Instead, the full power of the Servlet API is available, allowing Controllers to be general-purpose: a Controller is able to not only handle web user interface requests but also to process remoting protocols or to generate reports on demand.

  Controllers can easily be tested by passing in mock objects for the HttpServletRequest and HttpServletResponse objects as parameters to the `handleRequest` method. As a convenience, Spring ships with a set of Servlet API mocks that are suitable for testing any kind of web components, but are particularly suitable for testing Spring web controllers. In contrast to a Struts Action, there is no need to mock the ActionServlet or any other infrastructure; HttpServletRequest and HttpServletResponse are sufficient.

  If Controllers need to be aware of specific environment references, they can choose to implement specific awareness interfaces, just like any other bean in a Spring (web) application context can do, for example:

  - `org.springframework.context.ApplicationContextAware`
  - `org.springframework.context.ResourceLoaderAware`
  - `org.springframework.web.context.ServletContextAware`

  Such environment references can easily be passed in testing environments, through the corresponding setters defined in the respective awareness interfaces. In general, it is recommended to keep the dependencies as minimal as possible: for example, if all you need is resource loading, implement ResourceLoaderAware only. Alternatively, derive from the WebApplicationObjectSupport base class, which gives you all those references through convenient accessors - but requires an ApplicationContext reference on initialization.

  Controllers can optionally implement the `LastModified` interface.

  Author:
    Rod Johnson, Juergen Hoeller
  See Also:
    `LastModified`, `SimpleControllerHandlerAdapter`, `AbstractController`, `MockHttpServletRequest`, `MockHttpServletResponse`, `ApplicationContextAware`, `ResourceLoaderAware`, `ServletContextAware`, `WebApplicationObjectSupport`

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `ModelAndView` | `handleRequest(HttpServletRequest request, HttpServletResponse response)` Process the request and return a ModelAndView object which the DispatcherServlet will render.

- - ### Method Detail

    - #### handleRequest

          ModelAndView handleRequest(HttpServletRequest request,
                                   HttpServletResponse response)
                                     throws Exception

      Process the request and return a ModelAndView object which the DispatcherServlet will render. A `null` return value is not an error: It indicates that this object completed request processing itself, thus there is no ModelAndView to render.
      Parameters:
        `request` - current HTTP request
        `response` - current HTTP response
      Returns:
        a ModelAndView to render, or `null` if handled directly
      Throws:
        `Exception` - in case of errors