public interface Controller
HttpServletResponseinstances just like a
HttpServletbut is able to participate in an MVC workflow. Controllers are comparable to the notion of a Struts
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.
When a Controller has been found to handle the request, the
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
So actually, this method is the main entrypoint for the
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
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:
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
ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception
nullreturn value is not an error: It indicates that this object completed request processing itself, thus there is no ModelAndView to render.
request- current HTTP request
response- current HTTP response
nullif handled directly
Exception- in case of errors