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SpringMVC之HandlerMapping源码剖析
学习一种知识,我喜欢看看源码是怎么进行它们类之间的关系以及方法的调用,是怎么实现的。这样我才感觉踏实。
既然现在谈到HandlerMapping,我们先知道HandlerMapping的作用:HandlerMapping的作用就是解析请求链接,然后根据请求链接找到执行这个请求的类(HandlerMapping所说的handler,也就是我们写的Controller或是Action)。
现在我们来了解HandlerMapping的继承体系图:
至于我们在配置文件中配置的BeanNameUrlHandlerMapping或者是SimpleUrlHandlerMapping,他们的目的是一样的,只是通过请求链接来找handler的方式不一样。
我们再来看看更详细的继承关系:
HandlerMapping的使用主要分为两步:注册和查找。
注册是根据配置文件中的配置将一个字符串和一个Controller类以<key,value>的形式存入到Map中,这个key就是对应的url中的某个字段。
查找就是HandlerMapping根据url中的的某个字段,在Map中以这个字段为key值对应的Controller类,并将Controller类封装成一个HandlerExecutionChain对象,HandlerExecutionChain中除了有Controller对象外,还有一组拦截器。
现在我简单以SimpleUrlHandlerMapping为例子来分析HandlerMapping是如何根据请求链接找到Controller类的。
1.注册
<!-- SpringMVC中的HandlerMapping配置 配置映射器 --> <bean id="" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="mappings"> <props> <prop key="/*.do">helloword</prop> </props> </property> </bean> <!--配置处理器 --> <bean id="helloword" class="cn.controller.HelloController"> <property name="methodNameResolver" ref="nameResolver"> </property> </bean>
当我们第一次访问服务器的时候IOC容器会根据配置文件中的红色的部分生成一个Map<String, Object>,这个map里面的值就是{/*.do=/helloworld}。
SimpleUrlHandlerMapping的作用就是获取这个集合,然后根据这个集合里的value找到对应的bean,这样就可以把url中的某个字段和我们写的处理器对应起来。下面是SimpleUrlHandlerMapping中的关键源码
/** * Calls the {@link #registerHandlers} method in addition to the * superclass‘s initialization. */ @Override public void initApplicationContext() throws BeansException { super.initApplicationContext(); registerHandlers(this.urlMap); }
我们来看看HandlerMapping的父类
但是在这个类中没有initApplicationContext()方法,我们就再来看看AbstractUrlHandlerMapping的父类
的确,在这个类中有了我们想要的initApplicationContext()方法。
/** * Initializes the interceptors. * @see #extendInterceptors(java.util.List) * @see #initInterceptors() */ @Override protected void initApplicationContext() throws BeansException { extendInterceptors(this.interceptors); detectMappedInterceptors(this.adaptedInterceptors); initInterceptors(); }
这个方法就是初始化SpringMVC容器,并对handler进行注册,urlMap中的值根据上面的配置文件就是{/*.do=/helloWorld}的
现在我们一起来看registerHandlers方法,
/** * Register all handlers specified in the URL map for the corresponding paths. * @param urlMap Map with URL paths as keys and handler beans or bean names as values * @throws BeansException if a handler couldn‘t be registered * @throws IllegalStateException if there is a conflicting handler registered */ protected void registerHandlers(Map<String, Object> urlMap) throws BeansException { if (urlMap.isEmpty()) { logger.warn("Neither ‘urlMap‘ nor ‘mappings‘ set on SimpleUrlHandlerMapping"); } else { for (Map.Entry<String, Object> entry : urlMap.entrySet()) { String url = entry.getKey(); Object handler = entry.getValue(); // Prepend with slash if not already present. if (!url.startsWith("/")) { url = "/" + url; } // Remove whitespace from handler bean name. if (handler instanceof String) { handler = ((String) handler).trim(); } registerHandler(url, handler); } } }
主要是对urlMap中的key值进行了一些处理,要是没有“/”的就加上"/",去掉空格等处理。这个方法中的重点是调用了registerHandler(url, handler)这个方法,在这个方法是它的父类AbstractUrlHandlerMapping中的方法。
我们来看看AbstractUrlHandlerMapping中的registerHandler(url, handler)的方法
/** * Register the specified handler for the given URL path. * @param urlPath the URL the bean should be mapped to * @param handler the handler instance or handler bean name String * (a bean name will automatically be resolved into the corresponding handler bean) * @throws BeansException if the handler couldn‘t be registered * @throws IllegalStateException if there is a conflicting handler registered */ protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException { Assert.notNull(urlPath, "URL path must not be null"); Assert.notNull(handler, "Handler object must not be null"); Object resolvedHandler = handler; // Eagerly resolve handler if referencing singleton via name. if (!this.lazyInitHandlers && handler instanceof String) { String handlerName = (String) handler; if (getApplicationContext().isSingleton(handlerName)) { resolvedHandler = getApplicationContext().getBean(handlerName); } } Object mappedHandler = this.handlerMap.get(urlPath); if (mappedHandler != null) { if (mappedHandler != resolvedHandler) { throw new IllegalStateException( "Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath + "]: There is already " + getHandlerDescription(mappedHandler) + " mapped."); } } else { if (urlPath.equals("/")) { if (logger.isInfoEnabled()) { logger.info("Root mapping to " + getHandlerDescription(handler)); } setRootHandler(resolvedHandler); } else if (urlPath.equals("/*")) { if (logger.isInfoEnabled()) { logger.info("Default mapping to " + getHandlerDescription(handler)); } setDefaultHandler(resolvedHandler); } else { this.handlerMap.put(urlPath, resolvedHandler); if (logger.isInfoEnabled()) { logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler)); } } }
看registerHandler方法红色的部分大家,可以看出是根据SimpleUrlHandlerMapping中的urlMap中的value值在ioc容器中找到对应的bean,并将url的某个字段作为key值,bean作为value存入到AbstractUrlHandlerMapping的urlMap属性中去,这样就达到url的某个字段对应到具体的controller了的目的,当遇到有请求访问服务器的时候,就可以根据url找到具体的controller去执行这个请求了。
2.查找
在Dispatcher类中,根据配置文件对handlerMapping进行注册,即对handlerMapping的初始化。
protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context); <span style="color:#ff0000;">initHandlerMappings(context);</span> initHandlerAdapters(context); initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); initViewResolvers(context);
private void initHandlerMappings(ApplicationContext context) { this.handlerMappings = null; if (this.detectAllHandlerMappings) { // Find all HandlerMappings in the ApplicationContext, including ancestor contexts. <span style="color:#ff0000;">Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);</span> if (!matchingBeans.isEmpty()) { <span style="color:#ff0000;">this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());</span> // We keep HandlerMappings in sorted order. OrderComparator.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. } }
于在配置文件中有两种不同类型的handlerMapping,所以从ioc容器中读取出来的handlerMapping有两个,然后将这两个handlerMapping的实例放入Dodispatcher中的handlerMappings属性中。
下面一步就是真正的根据url中的某个字段到已经注册好了的Map<urlString,Controller>中找出执行这个url请求的Controller,用户的请求在被Dispatcher拦截后,会交给Dispatcher的doDispatch执行。在doDispatch方法中主要看红色标记的getHandler方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; int interceptorIndex = -1; try { ModelAndView mv; boolean errorView = false; try { processedRequest = checkMultipart(request); // Determine handler for the current request. <span style="color:#ff0000;">mappedHandler = getHandler(processedRequest, false);</span> if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. 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 (logger.isDebugEnabled()) { String requestUri = urlPathHelper.getRequestUri(request); logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } // Apply preHandle methods of registered interceptors. HandlerInterceptor[] interceptors = mappedHandler.getInterceptors(); if (interceptors != null) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) { triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); return; } interceptorIndex = i; } } // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); // Do we need view name translation? if (mv != null && !mv.hasView()) { mv.setViewName(getDefaultViewName(request)); } // Apply postHandle methods of registered interceptors. if (interceptors != null) { for (int i = interceptors.length - 1; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv); } } } catch (ModelAndViewDefiningException ex) { logger.debug("ModelAndViewDefiningException encountered", ex); mv = ex.getModelAndView(); } catch (Exception ex) { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(processedRequest, response, handler, ex); errorView = (mv != null); } // Did the handler return a view to render? if (mv != null && !mv.wasCleared()) { render(mv, processedRequest, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isDebugEnabled()) { logger.debug("Null ModelAndView returned to DispatcherServlet with name ‘" + getServletName() + "‘: assuming HandlerAdapter completed request handling"); } } // Trigger after-completion for successful outcome. triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null); }
getHandler方法主要会调用已经注册好了的handlerMapping中的getHandler方法
DispatcherServlet中的getHandler方法
/** * Return the HandlerExecutionChain for this request. * <p>Tries all handler mappings in order. * @param request current HTTP request * @return the HandlerExecutionChain, or {@code null} if no handler could be found */ protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { for (HandlerMapping hm : this.handlerMappings) { if (logger.isTraceEnabled()) { logger.trace( "Testing handler map [" + hm + "] in DispatcherServlet with name ‘" + getServletName() + "‘"); } HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) { return handler; } } return null; }
现在再来看看HandlerMapping的getHandler方法,可以看到HandlerMapping接口中只有一个getHandler方法
public interface HandlerMapping { /** * Name of the {@link HttpServletRequest} attribute that contains the path * within the handler mapping, in case of a pattern match, or the full * relevant URI (typically within the DispatcherServlet‘s mapping) else. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations. URL-based HandlerMappings will * typically support it, but handlers should not necessarily expect * this request attribute to be present in all scenarios. */ String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping"; /** * Name of the {@link HttpServletRequest} attribute that contains the * best matching pattern within the handler mapping. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations. URL-based HandlerMappings will * typically support it, but handlers should not necessarily expect * this request attribute to be present in all scenarios. */ String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern"; /** * Name of the boolean {@link HttpServletRequest} attribute that indicates * whether type-level mappings should be inspected. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations. */ String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping"; /** * Name of the {@link HttpServletRequest} attribute that contains the URI * templates map, mapping variable names to values. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations. URL-based HandlerMappings will * typically support it, but handlers should not necessarily expect * this request attribute to be present in all scenarios. */ String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables"; /** * Name of the {@link HttpServletRequest} attribute that contains a map with * URI matrix variables. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations and may also not be present depending on * whether the HandlerMapping is configured to keep matrix variable content * in the request URI. */ String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables"; /** * Name of the {@link HttpServletRequest} attribute that contains the set of * producible MediaTypes applicable to the mapped handler. * <p>Note: This attribute is not required to be supported by all * HandlerMapping implementations. Handlers should not necessarily expect * this request attribute to be present in all scenarios. */ String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes"; /** * Return a handler and any interceptors for this request. The choice may be made * on request URL, session state, or any factor the implementing class chooses. * <p>The returned HandlerExecutionChain contains a handler Object, rather than * even a tag interface, so that handlers are not constrained in any way. * For example, a HandlerAdapter could be written to allow another framework‘s * handler objects to be used. * <p>Returns {@code null} if no match was found. This is not an error. * The DispatcherServlet will query all registered HandlerMapping beans to find * a match, and only decide there is an error if none can find a handler. * @param request current HTTP request * @return a HandlerExecutionChain instance containing handler object and * any interceptors, or {@code null} if no mapping found * @throws Exception if there is an internal error */ HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception; }
再看看实现了HandlerMapping的AbstractHandlerMapping抽象类,AbstractHandlerMapping中的getHandler方法,这个方法的主要作用是根据url找到controller后,并将controller封装成一个HandlerExecutionChain对象
@Override public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { Object handler = getHandlerInternal(request); if (handler == null) { handler = getDefaultHandler(); } if (handler == null) { return null; } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request); if (CorsUtils.isCorsRequest(request)) { CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request); CorsConfiguration handlerConfig = getCorsConfiguration(handler, request); CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig); executionChain = getCorsHandlerExecutionChain(request, executionChain, config); } return executionChain; }
AbstractHandlerMapping的getHandlerInternal方法是个抽象方法,由AbstractHandlerMapping的子类AbstractUrlHandlerMapping实现
/** * Look up a handler for the given request, returning {@code null} if no * specific one is found. This method is called by {@link #getHandler}; * a {@code null} return value will lead to the default handler, if one is set. * <p>On CORS pre-flight requests this method should return a match not for * the pre-flight request but for the expected actual request based on the URL * path, the HTTP methods from the "Access-Control-Request-Method" header, and * the headers from the "Access-Control-Request-Headers" header thus allowing * the CORS configuration to be obtained via {@link #getCorsConfigurations}, * <p>Note: This method may also return a pre-built {@link HandlerExecutionChain}, * combining a handler object with dynamically determined interceptors. * Statically specified interceptors will get merged into such an existing chain. * @param request current HTTP request * @return the corresponding handler instance, or {@code null} if none found * @throws Exception if there is an internal error */ protected abstract Object getHandlerInternal(HttpServletRequest request) throws Exception;
AbstractUrlHandlerMapping实现类里面的getHandlerInternal方法
/** * Look up a handler for the URL path of the given request. * @param request current HTTP request * @return the handler instance, or {@code null} if none found */ @Override protected Object getHandlerInternal(HttpServletRequest request) throws Exception { String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); Object handler = lookupHandler(lookupPath, request); if (handler == null) { // We need to care for the default handler directly, since we need to // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well. Object rawHandler = null; if ("/".equals(lookupPath)) { rawHandler = getRootHandler(); } if (rawHandler == null) { rawHandler = getDefaultHandler(); } if (rawHandler != null) { // Bean name or resolved handler? if (rawHandler instanceof String) { String handlerName = (String) rawHandler; rawHandler = getApplicationContext().getBean(handlerName); } validateHandler(rawHandler, request); handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null); } } if (handler != null && logger.isDebugEnabled()) { logger.debug("Mapping [" + lookupPath + "] to " + handler); } else if (handler == null && logger.isTraceEnabled()) { logger.trace("No handler mapping found for [" + lookupPath + "]"); } return handler; }
getLookupPathForRequest方法主要是截取url中对应controller的那一部分,lookupHandler方法根据截取的url字段找到对应的controller,看到红色的部分就和我们注册handlerMapping的那一步相关了,我们早早的就将url的部分字段所对应的controller放到了AbstractUrlHandlerMapping中的handlerMap属性中了,现在就能根据url找到对应的controller了
/** * Look up a handler instance for the given URL path. * <p>Supports direct matches, e.g. a registered "/test" matches "/test", * and various Ant-style pattern matches, e.g. a registered "/t*" matches * both "/test" and "/team". For details, see the AntPathMatcher class. * <p>Looks for the most exact pattern, where most exact is defined as * the longest path pattern. * @param urlPath URL the bean is mapped to * @param request current HTTP request (to expose the path within the mapping to) * @return the associated handler instance, or {@code null} if not found * @see #exposePathWithinMapping * @see org.springframework.util.AntPathMatcher */ protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception { // Direct match? Object handler = this.handlerMap.get(urlPath); if (handler != null) { // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } validateHandler(handler, request); return buildPathExposingHandler(handler, urlPath, urlPath, null); } // Pattern match? List<String> matchingPatterns = new ArrayList<String>(); for (String registeredPattern : this.handlerMap.keySet()) { if (getPathMatcher().match(registeredPattern, urlPath)) { matchingPatterns.add(registeredPattern); } else if (useTrailingSlashMatch()) { if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) { matchingPatterns.add(registeredPattern +"/"); } } } String bestPatternMatch = null; Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath); if (!matchingPatterns.isEmpty()) { Collections.sort(matchingPatterns, patternComparator); if (logger.isDebugEnabled()) { logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns); } bestPatternMatch = matchingPatterns.get(0); } if (bestPatternMatch != null) { handler = this.handlerMap.get(bestPatternMatch); if (handler == null) { Assert.isTrue(bestPatternMatch.endsWith("/")); handler = this.handlerMap.get(bestPatternMatch.substring(0, bestPatternMatch.length() - 1)); } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } validateHandler(handler, request); String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath); // There might be multiple ‘best patterns‘, let‘s make sure we have the correct URI template variables // for all of them Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>(); for (String matchingPattern : matchingPatterns) { if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) { Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath); Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars); uriTemplateVariables.putAll(decodedVars); } } if (logger.isDebugEnabled()) { logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables); } return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables); } // No handler found... return null; }
到这里算是完了。但是大家可能感觉有点蒙,所以还总结了,方便记忆和理解
就对源码中是如何根据url找到对应的controller进行总结
1.SimpleUrlHandlerMapping根据配置文件中的SimpleUrlHandlerMapping的配置,获得一个map集合,map中存储的是{urlString=beanId}。SimpleUrlHandlerMapping调用父类
AbstractUrlHandlerMapping的registerHandler方法。
2.AbstractUrlHandlerMapping的registerHandler方法有SimpleUrlHandlerMapping传入的map中的urlString和beanId,并根据beanId找到对应的bean即controller,将urlString和urlString对应的controller放入AbstractUrlHandlerMapping的handlerMap中。
3.Dispatcher获取IOC容器中已经初始化好的HandlerMapping,再由HandlerMapping调用自己的getHandler方法根据请求返回HandlerExecutionChain对象。AbstractHandlerMapping方法实现了HandlerMapping接口的getHandler方法。AbstractHandlerMapping中的getHandler方法的主要作用是找到controller,并对controller进行封装成HandlerExecutionChain对象,HandlerExecutionChain中除了controller对象外,还有拦截器对象的集合。
4.AbstractHandlerMapping的getHandler方法中又 调用了AbstractHandlerMapping子类的AbstractUrlHandlerMapping getHandlerInternal方法。getHandlerInternal方法就是截取url中对应的controller字段,并以这个字段为key值去AbstractUrlHandlerMapping 的handlerMap中找寻对应的value,即controlle。
SpringMVC之HandlerMapping源码剖析