深入了解SpringMVC源码解析深入了解SpringMVC源码解析

Spring MVC源码解析
Spring MVC的使用原理其实是通过配置一个Servlet来接管所有的请求，所有的请求由这个Servlet来进行分发处理。
我们可以从web.xml里面看出这一点

springmvc org.springframework.web.servlet.DispatcherServlet contextConfigLocationclasspath:springmvc.xml

这个Servlet就是Spring MVC提供的DispatcherServlet，它的继承图如下：

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DispatcherServlet大致接收请求的时序图如下：

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下面我们先设定几个问题然后再去看源码。

DispatcherServlet初始化的时机？

我们将断点打在DispatcherServlet中的onRefresh方法上
，然后启动项目。

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从这个堆栈的图可以看出，最开始是HttpServletBean的init方法执行，然后启动Spring容器，Spring容器初始化的最后一步finishRefresh里面进行了事件通知。
FrameworkServlet里有个内部类ContextRefreshListener，实现了ApplicationListener接口，接收到了上面的事件通知，执行onApplicationEvent方法。

private class ContextRefreshListener implements ApplicationListener {@Override public void onApplicationEvent(ContextRefreshedEvent event) { FrameworkServlet.this.onApplicationEvent(event); } }

继续跟踪onApplicationEvent方法

public void onApplicationEvent(ContextRefreshedEvent event) { this.refreshEventReceived = true; synchronized (this.onRefreshMonitor) { onRefresh(event.getApplicationContext()); } }

发现最终是由onRefresh方法来进行具体处理的，并且这个onRefresh方法在FrameworkServlet里面是个空方法，是由它的子类DispatcherServlet来实现的。
我们来看DispatcherServlet里的onRefresh方法

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); }

这样就把SpringMVC的九大组件给初始化了。

我们的@RequestMapping注解在方法上，SpringMVC是怎么根据这个注解就能将对应的请求执行到这个方法上的？

从上面可以看到有个initHandlerMappings方法：

private void initHandlerMappings(ApplicationContext context) { this.handlerMappings = null; if (this.detectAllHandlerMappings) { // 找所有实现了HandlerMapping接口的类 Map matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false); if (!matchingBeans.isEmpty()) { this.handlerMappings = new ArrayList<>(matchingBeans.values()); // We keep HandlerMappings in sorted order. AnnotationAwareOrderComparator.sort(this.handlerMappings); } } else { try { HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class); this.handlerMappings = Collections.singletonList(hm); } catch (NoSuchBeanDefinitionException ex) { // Ignore, we'll add a default HandlerMapping later. } }// Ensure we have at least one HandlerMapping, by registering // a default HandlerMapping if no other mappings are found. if (this.handlerMappings == null) { //默认情况下，我们是使用的这个方法。 this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class); if (logger.isTraceEnabled()) { logger.trace("No HandlerMappings declared for servlet '" + getServletName() + "': using default strategies from DispatcherServlet.properties"); } } }

继续跟踪getDefaultStrategies方法

protected List getDefaultStrategies(ApplicationContext context, Class strategyInterface) { String key = strategyInterface.getName(); String value = https://www.it610.com/article/defaultStrategies.getProperty(key); if (value != null) { String[] classNames = StringUtils.commaDelimitedListToStringArray(value); List strategies = new ArrayList<>(classNames.length); for (String className : classNames) { try { Class clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader()); Object strategy = createDefaultStrategy(context, clazz); strategies.add((T) strategy); } //省略部分代码... } return strategies; } else { return new LinkedList<>(); } }

可以看出对classNames进行了遍历，这里有两个值，
BeanNameUrlHandlerMapping和RequestMappingHandlerMapping，我们一般用的是RequestMappingHandlerMapping。
RequestMappingHandlerMapping的父类AbstractHandlerMethodMapping实现了InitializingBean接口，我们来看看它实现的afterPropertiesSet方法。

public void afterPropertiesSet() { this.config = new RequestMappingInfo.BuilderConfiguration(); this.config.setUrlPathHelper(getUrlPathHelper()); this.config.setPathMatcher(getPathMatcher()); this.config.setSuffixPatternMatch(this.useSuffixPatternMatch); this.config.setTrailingSlashMatch(this.useTrailingSlashMatch); this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch); this.config.setContentNegotiationManager(getContentNegotiationManager()); super.afterPropertiesSet(); }

前面都是一些配置，后面是调用父类的afterPropertiesSet方法，此方法里只有initHandlerMethods一个方法

protected void initHandlerMethods() { for (String beanName : getCandidateBeanNames()) { if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) { processCandidateBean(beanName); } } handlerMethodsInitialized(getHandlerMethods()); }

主要看processCandidateBean方法

protected void processCandidateBean(String beanName) { Class beanType = null; try { beanType = obtainApplicationContext().getType(beanName); } catch (Throwable ex) { // An unresolvable bean type, probably from a lazy bean - let's ignore it. if (logger.isTraceEnabled()) { logger.trace("Could not resolve type for bean '" + beanName + "'", ex); } } if (beanType != null && isHandler(beanType)) { detectHandlerMethods(beanName); } }

继续跟踪detectHandlerMethods方法

protected void detectHandlerMethods(Object handler) { Class handlerType = (handler instanceof String ? obtainApplicationContext().getType((String) handler) : handler.getClass()); if (handlerType != null) { Class userType = ClassUtils.getUserClass(handlerType); //利用工具，取出类里面的方法并组装成map Map methods = MethodIntrospector.selectMethods(userType, (MethodIntrospector.MetadataLookup) method -> { try { return getMappingForMethod(method, userType); } catch (Throwable ex) { throw new IllegalStateException("Invalid mapping on handler class [" + userType.getName() + "]: " + method, ex); } }); if (logger.isTraceEnabled()) { logger.trace(formatMappings(userType, methods)); } //遍历map，处理里面的方法 methods.forEach((method, mapping) -> { Method invocableMethod = AopUtils.selectInvocableMethod(method, userType); registerHandlerMethod(handler, invocableMethod, mapping); }); } }

继续跟踪里面的register方法

public void register(T mapping, Object handler, Method method) { this.readWriteLock.writeLock().lock(); try { HandlerMethod handlerMethod = createHandlerMethod(handler, method); assertUniqueMethodMapping(handlerMethod, mapping); this.mappingLookup.put(mapping, handlerMethod); List directUrls = getDirectUrls(mapping); for (String url : directUrls) { this.urlLookup.add(url, mapping); }String name = null; if (getNamingStrategy() != null) { name = getNamingStrategy().getName(handlerMethod, mapping); addMappingName(name, handlerMethod); }CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping); if (corsConfig != null) { this.corsLookup.put(handlerMethod, corsConfig); }this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name)); } finally { this.readWriteLock.writeLock().unlock(); } }

可以看出mappingLookup、urlLookup、registry都放入了值。这时我也不知道每个的具体作用。我把断点打到这3个属性上。然后前端发起一个get请求。

请求匹配的过程？

前端发起请求，断点停在了AbstractHandlerMethodMapping.MappingRegistry#getMappingsByUrl方法上，以前端发起的请求路径，从urlLookup上获取对应的值。

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最后看看请求分发的主流程，也是springMVC最核心的代码

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { //multipart请求处理 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // 获取合适的HandlerExecutionChain mappedHandler = getHandler(processedRequest); if (mappedHandler == null) { noHandlerFound(processedRequest, response); return; }//获取合适的HandlerAdapter HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler. String method = request.getMethod(); boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } }if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; }// handle执行调用（核心） mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; }applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception ex) { dispatchException = ex; } catch (Throwable err) { // As of 4.3, we're processing Errors thrown from handler methods as well, // making them available for @ExceptionHandler methods and other scenarios. dispatchException = new NestedServletException("Handler dispatch failed", err); } //视图解析并渲染到页面 processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) { triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Throwable err) { triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", err)); } finally { if (asyncManager.isConcurrentHandlingStarted()) { // Instead of postHandle and afterCompletion if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else { // Clean up any resources used by a multipart request. if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }

总结：

tomcat的Servlet调起Spring容器启动，Spring容器启动完，事件通知到SpringMVC的DispatcherServlet。
这时会扫描所有的bean，将注解了@Controller和@RequestMapping的解析出来。
前端请求发过来，DispatcherServlet接收到（因为它是个servlet，配置在web.xml的），根据上一步处理好的映射关系，找到对应的方法来处理。

【深入了解SpringMVC源码解析】如通过/test能找到test方法

@RequestMapping("/test") public String test(String name, HttpServletRequest request,Model model){ System.out.println("name"); model.addAttribute("date",new Date()); return "success"; }