SpringMVC实现原理及详解

2018-07-16 02:38:55来源：博客园阅读 ()

1、Spring mvc介绍

SpringMVC框架是以请求为驱动，围绕Servlet设计，将请求发给控制器，然后通过模型对象，分派器来展示请求结果视图。其中核心类是DispatcherServlet，它是一个Servlet，顶层是实现的Servlet接口。

2、SpringMVC使用

需要在web.xml中配置DispatcherServlet。并且需要配置spring监听器ContextLoaderListene

 1 <listener>
 2             <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 3         </listener>        
 4         <servlet>
 5         <servlet-name>springmvc</servlet-name>
 6         <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 7                 <!-- 如果不设置init-param标签，则必须在/WEB-INF/下创建xxx-servlet.xml文件，其中xxx是servlet-name中配置的名称。  -->
 8                 <init-param>
 9             <param-name>contextConfigLocation</param-name>
10             <param-value>classpath:spring/springmvc-servlet.xml</param-value>
11         </init-param>
12         <load-on-startup>1</load-on-startup>
13     </servlet>
14     <servlet-mapping>
15         <servlet-name>springmvc</servlet-name>
16         <url-pattern>/</url-pattern>
17     </servlet-mapping>

3、SpringMVC运行原理

如图所示：

流程说明：

（1）客户端（浏览器）发送请求，直接请求到DispatcherServlet。

（2）DispatcherServlet根据请求信息调用HandlerMapping，解析请求对应的Handler。

（3）解析到对应的Handler后，开始由HandlerAdapter适配器处理。

（4）HandlerAdapter会根据Handler来调用真正的处理器开处理请求，并处理相应的业务逻辑。

（5）处理器处理完业务后，会返回一个ModelAndView对象，Model是返回的数据对象，View是个逻辑上的View。

（6）ViewResolver会根据逻辑View查找实际的View。

（7）DispaterServlet把返回的Model传给View。

（8）通过View返回给请求者（浏览器）

4、DispatcherServlet详细解析

首先看下源码：

  1 package org.springframework.web.servlet;
  2  
  3 @SuppressWarnings("serial")
  4 public class DispatcherServlet extends FrameworkServlet {
  5  
  6     public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
  7     public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
  8     public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
  9     public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
 10     public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
 11     public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
 12     public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
 13     public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
 14     public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";
 15     public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";
 16     public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";
 17     public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";
 18     public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";
 19     public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";
 20     public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";
 21     public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";
 22     public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() + ".EXCEPTION";
 23     public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";
 24     private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
 25     protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);
 26     private static final Properties defaultStrategies;
 27     static {
 28         try {
 29             ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
 30             defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
 31         }
 32         catch (IOException ex) {
 33             throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
 34         }
 35     }
 36  
 37     /** Detect all HandlerMappings or just expect "handlerMapping" bean? */
 38     private boolean detectAllHandlerMappings = true;
 39  
 40     /** Detect all HandlerAdapters or just expect "handlerAdapter" bean? */
 41     private boolean detectAllHandlerAdapters = true;
 42  
 43     /** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean? */
 44     private boolean detectAllHandlerExceptionResolvers = true;
 45  
 46     /** Detect all ViewResolvers or just expect "viewResolver" bean? */
 47     private boolean detectAllViewResolvers = true;
 48  
 49     /** Throw a NoHandlerFoundException if no Handler was found to process this request? **/
 50     private boolean throwExceptionIfNoHandlerFound = false;
 51  
 52     /** Perform cleanup of request attributes after include request? */
 53     private boolean cleanupAfterInclude = true;
 54  
 55     /** MultipartResolver used by this servlet */
 56     private MultipartResolver multipartResolver;
 57  
 58     /** LocaleResolver used by this servlet */
 59     private LocaleResolver localeResolver;
 60  
 61     /** ThemeResolver used by this servlet */
 62     private ThemeResolver themeResolver;
 63  
 64     /** List of HandlerMappings used by this servlet */
 65     private List<HandlerMapping> handlerMappings;
 66  
 67     /** List of HandlerAdapters used by this servlet */
 68     private List<HandlerAdapter> handlerAdapters;
 69  
 70     /** List of HandlerExceptionResolvers used by this servlet */
 71     private List<HandlerExceptionResolver> handlerExceptionResolvers;
 72  
 73     /** RequestToViewNameTranslator used by this servlet */
 74     private RequestToViewNameTranslator viewNameTranslator;
 75  
 76     private FlashMapManager flashMapManager;
 77  
 78     /** List of ViewResolvers used by this servlet */
 79     private List<ViewResolver> viewResolvers;
 80  
 81     public DispatcherServlet() {
 82         super();
 83     }
 84  
 85     public DispatcherServlet(WebApplicationContext webApplicationContext) {
 86         super(webApplicationContext);
 87     }
 88     @Override
 89     protected void onRefresh(ApplicationContext context) {
 90         initStrategies(context);
 91     }
 92  
 93     protected void initStrategies(ApplicationContext context) {
 94         initMultipartResolver(context);
 95         initLocaleResolver(context);
 96         initThemeResolver(context);
 97         initHandlerMappings(context);
 98         initHandlerAdapters(context);
 99         initHandlerExceptionResolvers(context);
100         initRequestToViewNameTranslator(context);
101         initViewResolvers(context);
102         initFlashMapManager(context);
103     }
104 }