org.springframework.web.servlet.mvc
Interface Controller

All Known Implementing Classes:

AbstractController, BurlapServiceExporter, HessianServiceExporter, HttpInvokerServiceExporter, UrlFilenameViewController

public interface Controller

Base Controller interface, representing a component that receives HttpServletRequest and HttpServletResponse like a HttpServlet but is able to participate in an MVC workflow. 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 Controller in an easy, Controllers are usually JavaBeans.

Workflow

After the DispatcherServlet has received a request and has done its work to resolve locales, themes and things a like, it tries to resolve a Controller, using a HandlerMapping. When a Controller has been found, the handleRequest method will be invoked, which is 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. This method - and also this interface - should preferrably not be implemented by custom controllers directly, since abstract controller also provided by this package already provide a lot of functionality for typical use cases in web applications. A few examples of those controllers: AbstractController, AbstractCommandController, SimpleFormController.

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 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: not only to handle web user interface requests but also to process remoting protocols or to generate reports on demand.

Controllers can easily be tested through passing in mock objects for servlet request and response. For 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.

Author:

Rod Johnson

See Also:

SimpleControllerHandlerAdapter, AbstractController, AbstractCommandController, SimpleFormController, HessianServiceExporter, BurlapServiceExporter, HttpInvokerServiceExporter, MockHttpServletRequest, MockHttpServletResponse, ApplicationContextAware, ResourceLoaderAware, ServletContextAware, WebApplicationObjectSupport

Method Summary

ModelAndView

handleRequest(HttpServletRequest request, HttpServletResponse response) Process the request and return a ModelAndView object which the DispatcherServlet will render.

Method Detail

handleRequest

public ModelAndView handleRequest(HttpServletRequest request,
                                  HttpServletResponse response)
                           throws Exception

Process the request and return a ModelAndView object which the DispatcherServlet will render. A null return 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