001/* 002 * Copyright 2002-2014 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.web.servlet.mvc; 018 019import javax.servlet.http.HttpServletRequest; 020import javax.servlet.http.HttpServletResponse; 021 022import org.springframework.web.servlet.ModelAndView; 023 024/** 025 * Base Controller interface, representing a component that receives 026 * {@code HttpServletRequest} and {@code HttpServletResponse} 027 * instances just like a {@code HttpServlet} but is able to 028 * participate in an MVC workflow. Controllers are comparable to the 029 * notion of a Struts {@code Action}. 030 * 031 * <p>Any implementation of the Controller interface should be a 032 * <i>reusable, thread-safe</i> class, capable of handling multiple 033 * HTTP requests throughout the lifecycle of an application. To be able to 034 * configure a Controller easily, Controller implementations are encouraged 035 * to be (and usually are) JavaBeans. 036 * 037 * <h3><a name="workflow">Workflow</a></h3> 038 * 039 * <p>After a {@code DispatcherServlet} has received a request and has 040 * done its work to resolve locales, themes, and suchlike, it then tries 041 * to resolve a Controller, using a 042 * {@link org.springframework.web.servlet.HandlerMapping HandlerMapping}. 043 * When a Controller has been found to handle the request, the 044 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest} 045 * method of the located Controller will be invoked; the located Controller 046 * is then responsible for handling the actual request and — if applicable 047 * — returning an appropriate 048 * {@link org.springframework.web.servlet.ModelAndView ModelAndView}. 049 * So actually, this method is the main entry point for the 050 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet} 051 * which delegates requests to controllers. 052 * 053 * <p>So basically any <i>direct</i> implementation of the {@code Controller} interface 054 * just handles HttpServletRequests and should return a ModelAndView, to be further 055 * interpreted by the DispatcherServlet. Any additional functionality such as 056 * optional validation, form handling, etc. should be obtained through extending 057 * {@link org.springframework.web.servlet.mvc.AbstractController AbstractController} 058 * or one of its subclasses. 059 * 060 * <h3>Notes on design and testing</h3> 061 * 062 * <p>The Controller interface is explicitly designed to operate on HttpServletRequest 063 * and HttpServletResponse objects, just like an HttpServlet. It does not aim to 064 * decouple itself from the Servlet API, in contrast to, for example, WebWork, JSF or Tapestry. 065 * Instead, the full power of the Servlet API is available, allowing Controllers to be 066 * general-purpose: a Controller is able to not only handle web user interface 067 * requests but also to process remoting protocols or to generate reports on demand. 068 * 069 * <p>Controllers can easily be tested by passing in mock objects for the 070 * HttpServletRequest and HttpServletResponse objects as parameters to the 071 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest} 072 * method. As a convenience, Spring ships with a set of Servlet API mocks 073 * that are suitable for testing any kind of web components, but are particularly 074 * suitable for testing Spring web controllers. In contrast to a Struts Action, 075 * there is no need to mock the ActionServlet or any other infrastructure; 076 * mocking HttpServletRequest and HttpServletResponse is sufficient. 077 * 078 * <p>If Controllers need to be aware of specific environment references, they can 079 * choose to implement specific awareness interfaces, just like any other bean in a 080 * Spring (web) application context can do, for example: 081 * <ul> 082 * <li>{@code org.springframework.context.ApplicationContextAware}</li> 083 * <li>{@code org.springframework.context.ResourceLoaderAware}</li> 084 * <li>{@code org.springframework.web.context.ServletContextAware}</li> 085 * </ul> 086 * 087 * <p>Such environment references can easily be passed in testing environments, 088 * through the corresponding setters defined in the respective awareness interfaces. 089 * In general, it is recommended to keep the dependencies as minimal as possible: 090 * for example, if all you need is resource loading, implement ResourceLoaderAware only. 091 * Alternatively, derive from the WebApplicationObjectSupport base class, which gives 092 * you all those references through convenient accessors but requires an 093 * ApplicationContext reference on initialization. 094 * 095 * <p>Controllers can optionally implement the {@link LastModified} interface. 096 * 097 * @author Rod Johnson 098 * @author Juergen Hoeller 099 * @see LastModified 100 * @see SimpleControllerHandlerAdapter 101 * @see AbstractController 102 * @see org.springframework.mock.web.MockHttpServletRequest 103 * @see org.springframework.mock.web.MockHttpServletResponse 104 * @see org.springframework.context.ApplicationContextAware 105 * @see org.springframework.context.ResourceLoaderAware 106 * @see org.springframework.web.context.ServletContextAware 107 * @see org.springframework.web.context.support.WebApplicationObjectSupport 108 */ 109public interface Controller { 110 111 /** 112 * Process the request and return a ModelAndView object which the DispatcherServlet 113 * will render. A {@code null} return value is not an error: it indicates that 114 * this object completed request processing itself and that there is therefore no 115 * ModelAndView to render. 116 * @param request current HTTP request 117 * @param response current HTTP response 118 * @return a ModelAndView to render, or {@code null} if handled directly 119 * @throws Exception in case of errors 120 */ 121 ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception; 122 123}