SpringMvc源码-RequestMappingHandlerMapping

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RequestMappingHandlerMapping负责将RequestMapping注解的方法与url关联起来，并且返回HandlerExecutionChain

加载过程

DispatcherServlet.initStrategies的initHandlerMappings方法中会通过读取DispatchServerlet.proeprties对HandlerMapping进行初始化，这里重点看RequestMappingHandlerMapping类

DispatcherServlet.properties的值

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org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
	org.springframework.web.servlet.function.support.RouterFunctionMapping

初始化HandlerMapping

HandlerMapping，封装了是request与他的处理类HandlerMethod的映射关系，他的职责主要是通过request找到对应的handlerMapping

AbstractHandlerMethodMapping实现了InitializingBean所以在afterPropertiesSet会进行初始化工作

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public void afterPropertiesSet() {
	//调用initHandlerMethods
	initHandlerMethods();
}

 //从ApplicationContext扫描所有的bean, 找到并且将handler method注册到容器中【将url和handlerMethod关联】
 protected void initHandlerMethods() {
	//获取application中所有的bean
	for (String beanName : getCandidateBeanNames()) {
		if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
       		//重点方法
			processCandidateBean(beanName);
		}
	}
	handlerMethodsInitialized(getHandlerMethods());
}

重点方法：processCandidateBean

根据bean找到method，封装成handlerMethod注册到容器中

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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);
		}
	}
	//这里isHandler判断beanType是否是一个Controller【判断是否有@Controller和@RequestMapping注解】
	if (beanType != null && isHandler(beanType)) {
     		//重点方法
		detectHandlerMethods(beanName);
	}
}

重点方法

detectHandlerMethods遍历bean的method方法

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protected void detectHandlerMethods(Object handler) {
		Class<?> handlerType = (handler instanceof String ?
				obtainApplicationContext().getType((String) handler) : handler.getClass());

		if (handlerType != null) {
			Class<?> userType = ClassUtils.getUserClass(handlerType);
			//遍历handler中的方法，通过getMappingForMethod返回RequestMappingInfo
			// 通过方法上的RequestMapping注解,生成RequestMappingInfo，并且和Method关联
			Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
					(MethodIntrospector.MetadataLookup<T>) 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method-->RequestMappingInfo 并且将method和mapping注册到 mappingRegistry中RequestMappingHandlerMapping对其进行了改写
			methods.forEach((method, mapping) -> {
				Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
				registerHandlerMethod(handler, invocableMethod, mapping);
			});
		}
	}

重点方法：registerHandlerMethod(handler, invocableMethod, mapping)

向容器注册HandlerMapping：registerHandlerMethod(handler, invocableMethod, mapping);
这里的mappingRegistry 是AbstractHandlerMethodMapping的内部类MappingRegistry;

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protected void registerHandlerMethod(Object handler, Method method, T mapping) {
	this.mappingRegistry.register(mapping, handler, method);
}

	public void register(T mapping, Object handler, Method method) {
		// Assert that the handler method is not a suspending one.
		if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
			throw new IllegalStateException("Unsupported suspending handler method detected: " + method);
		}
		this.readWriteLock.writeLock().lock();
		try {
			//封装成HandlerMethod
			HandlerMethod handlerMethod = createHandlerMethod(handler, method);
			//判断mapping是否已经存在，存在抛异常
			validateMethodMapping(handlerMethod, mapping);
			//关联 mapping-->handlerMethod
			this.mappingLookup.put(mapping, handlerMethod);
			//根据mapping获取url并且将Url和mapping关联起来
			List<String> directUrls = getDirectUrls(mapping);
			for (String url : directUrls) {
				this.urlLookup.add(url, mapping);
			}

			//关联name【RequestMappingInfoHandlerMethodMappingNamingStrategy.getName】和handlerMethod
			String name = null;
			if (getNamingStrategy() != null) {
				name = getNamingStrategy().getName(handlerMethod, mapping);
				addMappingName(name, handlerMethod);
			}

			//corsLookup绑定handlerMethod和corsConfig,注解或者方法上带CrossOrigin
			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();
		}
	}

至此所有的RequestMapping都注册到容器中

doDipatch时候

通过reqeust获取handler和拦截器封装成HandlerExecutionChain过程

找到在初始化时候注册的handlerMappings，调用它们的getHandler方法，具体实现在AbstraceHanlderMapping中

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public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
	//根据request获取一个指定的handler，如果没找到返回null，类型是HandlerMethod，调用链路RequestMappingHandlerMapping.getHandlerInternal-->AbstractHandlerMethodMapping.getgetHandlerInternal
	
	//重点方法1 
	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 = obtainApplicationContext().getBean(handlerName);
	}

	//重点方法2 返回HandlerExecutionChain【handler和拦截器】的封装
	HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

	if (logger.isTraceEnabled()) {
		logger.trace("Mapped to " + handler);
	} else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
		logger.debug("Mapped to " + executionChain.getHandler());
	}

	if (hasCorsConfigurationSource(handler)) {
		CorsConfiguration config = (this.corsConfigurationSource != null ? this.corsConfigurationSource.getCorsConfiguration(request) : null);
		CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
		config = (config != null ? config.combine(handlerConfig) : handlerConfig);
		executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
	}

	return executionChain;
}

重点方法1 getHandlerInternal

这里的实现见：AbstractHandlerMethodMapping.getgetHandlerInternal

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@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
	//获取urlPath用于查找HandlerMethod
	String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
	request.setAttribute(LOOKUP_PATH, lookupPath);
	this.mappingRegistry.acquireReadLock();
	try {
		//查找HandlerMethod 优先通过Path找，没找到轮询mappingLookup，之后对找到的HandlerMethod排序找到最合适的HandlerMethod
		HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
		//re-create bean 享元模式防止请求修改HandlerMethod
		return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
	} finally {
		this.mappingRegistry.releaseReadLock();
	}
}

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
	//
	List<Match> matches = new ArrayList<>();
	//通过path查找到符合要求的RequestMappingInfo
	List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
	if (directPathMatches != null) {
		addMatchingMappings(directPathMatches, matches, request);
	}

	//如果通过path没找到去mappingLookup轮询一遍查找
	if (matches.isEmpty()) {
		// No choice but to go through all mappings...
		addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
	}

	//不为空
	if (!matches.isEmpty()) {
		//根据RequestMappingInfoHandlerMapping.getMappingComparator排序Match.mapping的Compare然后取第一个
		// todo 优先级未看
		Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
		matches.sort(comparator);
		//排序后取第一个作为返回结果
		Match bestMatch = matches.get(0);
		//取出来俩个然后优先级一样直接抛出异常意思是Handler重复"多个优先级"
		if (matches.size() > 1) {
			if (logger.isTraceEnabled()) {
				logger.trace(matches.size() + " matching mappings: " + matches);
			}
			if (CorsUtils.isPreFlightRequest(request)) {
				return PREFLIGHT_AMBIGUOUS_MATCH;
			}
			Match secondBestMatch = matches.get(1);
			if (comparator.compare(bestMatch, secondBestMatch) == 0) {
				Method m1 = bestMatch.handlerMethod.getMethod();
				Method m2 = secondBestMatch.handlerMethod.getMethod();
				String uri = request.getRequestURI();
				throw new IllegalStateException(
						"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
			}
		}
		request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
		//为request设置值：PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE，返回对应的handlerMethod
		//这里其实就是把mapping,和handler都返回只不过mapping放在了requst里
		handleMatch(bestMatch.mapping, lookupPath, request);
		return bestMatch.handlerMethod;
	} else {
		//都没匹配到调用该方法见RequestMappingInfoHandlerMapping，其中不符合RequestMappingInfo的会抛异常
		return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
	}
}

重点方法2 getHandlerExecutionChain

返回handler和拦截器的封装，注：springboot的WebMvcConfigurer.addInterceptors方法中添加的拦截器会转成MappedInterceptor添加到RRequestMappingHandlerMapping中代码可以从WebMvcAutoConfiguration中看

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protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
	//如果是一个存在的HandlerExecutionChain,直接返回，否则new一个HandlerExecutionChain
	//new HandlerExecutionChain(handler)在HandlerExecutionChain的构造方法里会再判断下Handler的类型，
	// 如果是HandlerExecutionChain进行merge
	// 如果是HandlerMethod会进行赋值具体见HandlerExecutionChain构造方法
	HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
			(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));

	String lookupPath = this.urlPathHelper.getLookupPathForRequest(request, LOOKUP_PATH);
	//处理拦截器，
	// 如果是MappedInterceptor，判断lookupPath是否匹配如果匹配将拦截器加入到HandlerExecutionChain
	// 如果是HandlerInterceptor 或者WebRequestInterceptor直接将拦截器加入到HandlerExecutionChain
	// todo 注意：springboot 通过WebMvcConfigurer配置的interceptor最终都会转成MappedInterceptor，
	// 见InterceptorRegistration.getInterceptor(),入口在WebMvcAutoConfiguration.requestMappingHandlerMapping()方法
	for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
		if (interceptor instanceof MappedInterceptor) {
			MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
			if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
				chain.addInterceptor(mappedInterceptor.getInterceptor());
			}
		} else {
			chain.addInterceptor(interceptor);
		}
	}
	return chain;
}

返回了包含handler和interceptor的HandlerExecutionChain为下一步handlerAdapter执行做好准备

附录：MappingRegistry几个重要的容器

上面提到的register过程中涉及到了MappingRegistry类，它包含了几个重要容器用来缓存url,RequestMappingInfo HandlerMethod的对应关系

  • urlLookup: url–>List<RequestMappingInfo>
  • mappingLookup:RequestMappingInfo–>HandlerMethod

附录：@RequestMapping注解

RequestMapping是一个用来处理请求地址映射的注解，可用于类或方法上。用于类上，表示类中的所有响应请求的方法都是以该地址作为父路径。

  • value：指定请求的实际地址，指定的地址可以是URI Template 模式（后面将会说明）；
  • method：指定请求的method类型， GET、POST、PUT、DELETE等；
  • consumes：指定处理请求的提交内容类型（Content-Type），例如application/json, text/html;
  • produces：指定返回的内容类型，仅当request请求头中的(Accept)类型中包含该指定类型才返回；
  • params：指定request中必须包含某些参数值是，才让该方法处理。
  • headers：指定request中必须包含某些指定的header值，才能让该方法处理请求。