首先看下 DispatcherServlet 源码：
代码语言：javascript复制package org.springframework.web.servlet;
@SuppressWarnings("serial")
public class DispatcherServlet extends FrameworkServlet {
public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";
public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() ".CONTEXT";
public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() ".LOCALE_RESOLVER";
public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() ".THEME_RESOLVER";
public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() ".THEME_SOURCE";
public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() ".INPUT_FLASH_MAP";
public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() ".OUTPUT_FLASH_MAP";
public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() ".FLASH_MAP_MANAGER";
public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() ".EXCEPTION";
public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);
private static final Properties defaultStrategies;
static {
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " ex.getMessage());
}
}
/** Detect all HandlerMappings or just expect "handlerMapping" bean? */
private boolean detectAllHandlerMappings = true;
/** Detect all HandlerAdapters or just expect "handlerAdapter" bean? */
private boolean detectAllHandlerAdapters = true;
/** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean? */
private boolean detectAllHandlerExceptionResolvers = true;
/** Detect all ViewResolvers or just expect "viewResolver" bean? */
private boolean detectAllViewResolvers = true;
/** Throw a NoHandlerFoundException if no Handler was found to process this request? **/
private boolean throwExceptionIfNoHandlerFound = false;
/** Perform cleanup of request attributes after include request? */
private boolean cleanupAfterInclude = true;
/** MultipartResolver used by this servlet */
private MultipartResolver multipartResolver;
/** LocaleResolver used by this servlet */
private LocaleResolver localeResolver;
/** ThemeResolver used by this servlet */
private ThemeResolver themeResolver;
/** List of HandlerMappings used by this servlet */
private List<HandlerMapping> handlerMappings;
/** List of HandlerAdapters used by this servlet */
private List<HandlerAdapter> handlerAdapters;
/** List of HandlerExceptionResolvers used by this servlet */
private List<HandlerExceptionResolver> handlerExceptionResolvers;
/** RequestToViewNameTranslator used by this servlet */
private RequestToViewNameTranslator viewNameTranslator;
private FlashMapManager flashMapManager;
/** List of ViewResolvers used by this servlet */
private List<ViewResolver> viewResolvers;
public DispatcherServlet() {
super();
}
public DispatcherServlet(WebApplicationContext webApplicationContext) {
super(webApplicationContext);
}
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
}DispatcherServlet 类中的属性 beans：
- HandlerMapping：用于 handlers 映射请求和一系列的对于拦截器的前处理和后处理，大部分用 @Controller 注解。
- HandlerAdapter：帮助 DispatcherServlet 处理映射请求处理程序的适配器，而不用考虑实际调用的是哪个处理程序。
- ViewResolver：根据配置解析实际的 View 类型。
- ThemeResolver：解决 Web 应用程序可以使用的主题，例如提供个性化布局。
- MultipartResolver：解析多部分请求，以支持从 HTML 表单上传文件。
- FlashMapManager：存储并检索可用于将一个请求属性传递到另一个请求的 input 和 output 的 FlashMap，通常用于重定向。
在 Web MVC 框架中，每个 DispatcherServlet 都拥有自己的 WebApplicationContext，它继承了 ApplicationContext。WebApplicationContext 包含了其上下文和 Servlet 实例之间共享的所有 beans。
1. HandlerMapping 接口 - 处理请求的映射
- SimpleUrlHandlerMapping：通过配置文件把 URL 映射到 Controller 类。
- DefaultAnnotationHandlerMapping：通过注解把 URL 映射到 Controller 类。
HandlerMapping
2. HandlerAdapter 接口 - 处理请求映射
AnnotationMethodHandlerAdapter：通过注解，把请求 URL 映射到 Controller 类的方法上。
HandlerAdapter
3. HandlerExceptionResolver 接口 - 异常处理
- SimpleMappingExceptionResolver：通过配置文件进行异常处理。
- AnnotationMethodHandlerExceptionResolver：通过注解进行异常处理。
HandlerExceptionResolver
4. ViewResolver 接口 - 解析 View 视图
UrlBasedViewResolver：通过配置文件，把一个视图名交给一个 View 来处理。
ViewResolver
