/*
* Copyright 2002-2006 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.web.servlet.mvc;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
/**
* Base Controller interface, representing a component that receives
* <code>HttpServletRequest</code> and <code>HttpServletResponse</code>
* instances just like a <code>HttpServlet</code> but is able to
* participate in an MVC workflow. Controllers are comparable to the
* notion of a Struts <code>Action</code>.
*
* <p>Any implementation of the Controller interface should be a
* <i>reusable, thread-safe</i> 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.
* </p>
*
* <p><b><a name="workflow">Workflow</a></b></p>
*
* <p>
* After a <cde>DispatcherServlet</code> has received a request and has
* done its work to resolve locales, themes and suchlike, it then tries
* to resolve a Controller, using a
* {@link org.springframework.web.servlet.HandlerMapping HandlerMapping}.
* When a Controller has been found to handle the request, the
* {@link #handleRequest(HttpServletRequest, HttpServletResponse) 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
* {@link org.springframework.web.servlet.ModelAndView ModelAndView}.
* So actually, this method is the main entrypoint for the
* {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
* which delegates requests to controllers. This method - and also this interface -
* should preferrably not be implemented by custom controllers <i>directly</i>, 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:
* {@link AbstractController AbstractController},
* {@link AbstractCommandController AbstractCommandController},
* {@link SimpleFormController SimpleFormController}.</p>
*
* <p>So basically any <i>direct</i> 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.</p>
*
* <p><b>Notes on design and testing</b></p>
*
* <p>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.</p>
*
* <p>Controllers can easily be tested by passing in mock objects for the
* HttpServletRequest and HttpServletResponse objects as parameters to the
* {@link #handleRequest(HttpServletRequest, HttpServletResponse) 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.</p>
*
* <p>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:</p>
* <ul>
* <li><code>org.springframework.context.ApplicationContextAware</code></li>
* <li><code>org.springframework.context.ResourceLoaderAware</code></li>
* <li><code>org.springframework.web.context.ServletContextAware</code></li>
* </ul>
*
* <p>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.
*
* <p>Controllers can optionally implement the LastModified interface.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see LastModified
* @see SimpleControllerHandlerAdapter
* @see AbstractController
* @see AbstractCommandController
* @see SimpleFormController
* @see org.springframework.mock.web.MockHttpServletRequest
* @see org.springframework.mock.web.MockHttpServletResponse
* @see org.springframework.context.ApplicationContextAware
* @see org.springframework.context.ResourceLoaderAware
* @see org.springframework.web.context.ServletContextAware
* @see org.springframework.web.context.support.WebApplicationObjectSupport
*/
public interface Controller {
/**
* Process the request and return a ModelAndView object which the DispatcherServlet
* will render. A <code>null</code> return value is not an error: It indicates that
* this object completed request processing itself, thus there is no ModelAndView
* to render.
* @param request current HTTP request
* @param response current HTTP response
* @return a ModelAndView to render, or <code>null</code> if handled directly
* @throws Exception in case of errors
*/
ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
}