public interface Controller
instances just like a
HttpServlet but 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.
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
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 entry point for the
which delegates requests to controllers.
So basically any direct implementation of the
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
or one of its subclasses.
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;
mocking HttpServletRequest and HttpServletResponse is 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
@Nullable ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws java.lang.Exception
null return value is not an error: it indicates that
this object completed request processing itself and that there is therefore no
ModelAndView to render.
request - current HTTP request
response - current HTTP response
null if handled directly
java.lang.Exception - in case of errors