springmvc path请求映射到bean 方法的流程

一、加载注册流程

1.在dispatch-servlet.xml中配置< mvc:annotation-driven/>，在控制器的方法上加入@RequestMapping注解即可。

2.mvc:annotation-driven的解析流程 会调用到自定义元素解析器的AnnotationDrivenBeanDefinitionParser.parse方法。

3.org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping为RequestMapping注解映射到后台接口的注册表。此类实现了InitializingBean接口，会触发到

afterPropertiesSet方法。

org.springframework.web.servlet.handler.AbstractHandlerMethodMapping
 
@Override
	public void afterPropertiesSet() {
		initHandlerMethods();
	}
 
	/**
	 * Scan beans in the ApplicationContext, detect and register handler methods.
	 * @see #getCandidateBeanNames()
	 * @see #processCandidateBean
	 * @see #handlerMethodsInitialized
	 */
	protected void initHandlerMethods() {
		for (String beanName : getCandidateBeanNames()) {
			if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
				processCandidateBean(beanName);
			}
		}
		handlerMethodsInitialized(getHandlerMethods());
	}

4.在initHandlerMethods方法中会先调用getCandidateBeanNames获取当前容器工厂的所有BEAN,然后逐个BEAN进行处理。

4.1 获取所有BEAN流程

protected String[] getCandidateBeanNames() {
		return (this.detectHandlerMethodsInAncestorContexts ?
				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
				obtainApplicationContext().getBeanNamesForType(Object.class));
	}

4.2 处理BEAN流程

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);
		}
	}

4.3 判断当前BEAN是否HANDLER

protected boolean isHandler(Class beanType) {
		return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
				AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
	}

4.4 如果此类是控制器或者有requestMapping注解，才会处理。

4.5 遍历当前类的所有方法，查找包含RequestMapping注解的方法，然后保存到

AbstractHandlerMethodMapping.MappingRegistry注册表中。

protected void detectHandlerMethods(Object handler) {
		Class handlerType = (handler instanceof String ?
				obtainApplicationContext().getType((String) handler) : handler.getClass());
 
		if (handlerType != null) {
			Class userType = ClassUtils.getUserClass(handlerType);
			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));
			}
			methods.forEach((method, mapping) -> {
				Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
				registerHandlerMethod(handler, invocableMethod, mapping);
			});
		}
	}

判断当前方法是否包含requestMapping注解

private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) {
		RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
		RequestCondition condition = (element instanceof Class ?
				getCustomTypeCondition((Class) element) : getCustomMethodCondition((Method) element));
		return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);
	}

最终会调用org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.registerHandlerMethod保存到URL和RequestMappinfo的映射注册表中。

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

具体的保存逻辑

在这个方法中主要操作的数据对象有四个，分别是mappingLookup、urlLookup、corsLookup和registry。下面对这四个对象进行说明:

1. mappingLookup对象是Map结构，key表示mapping对象，value表示处理对象，在本例中key是RequestMappingInfo对象，value是Controller中的某一个方法。
2. urlLookup对象是Map结构，key表示url，value表示mapping对象，本例中key是具体的url值"/demo/postMapping/"，value是RequestMappingInfo对象，
3. corsLookup对象是Map结构，key表示处理方法（Controller中的某个方法），value表示跨域配置，本例中没有进行跨域注解的使用因此数据不存在，如果需要看到跨域数据，可以在method上添加@CrossOrigin注解
4. registry对象是Map结构，key表示mapping对象，value表示MappingRegistration对象

AbstractHandlerMethodMapping.MappingRegistry  内部类
public void register(T mapping, Object handler, Method method) {
 
			this.readWriteLock.writeLock().lock();
			try {
				HandlerMethod handlerMethod = createHandlerMethod(handler, method);
				validateMethodMapping(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);
				}
 
			
 
				this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name));
			}
			finally {
				this.readWriteLock.writeLock().unlock();
			}
		}

生成的数据如下：

5.系统拦截器列表初始化过程,会调用到AbstractHandlerMapping.initApplicationContext，这个会查找当前容器工厂中所有继承了MappedInterceptor类的拦截器实例BEAN.然后保存到AbstractHandlerMapping.interceptors

protected void initApplicationContext() throws BeansException {
		extendInterceptors(this.interceptors);
		detectMappedInterceptors(this.adaptedInterceptors);
		initInterceptors();
	}

二、调用HTTP请求根据PATH寻找接口方法流程

1.首先tomcat会调用DispatcherServlet.doDispatch方法，进行请求分发处理。

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 {
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);
 
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
 
				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
 
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}
 
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
 
				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}
 
				applyDefaultViewName(processedRequest, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
		
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
	
		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);
				}
			}
		}
	}

2.首先调用getHandler去根据请求PATH查找HandlerExecutionChain，HandlerExecutionChain就是一个RequestHandleMappinfo加上一个拦截器列表。会调用到AbstractHandlerMapping.getHandler

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 = obtainApplicationContext().getBean(handlerName);
		}
 
		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
 
		return executionChain;
	}

3.最终会调用到AbstractHandlerMapping.lookupHandlerMethod根据PATH查找HandlerMethod，这里面的 this.mappingRegistry.getMappingsByUrl就是初始化时的URL和RequestMappingInfo映射表。

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List matches = new ArrayList<>();
		List directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
		if (directPathMatches != null) {
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {
			// No choice but to go through all mappings...
			addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
		}
 
		if (!matches.isEmpty()) {
			Match bestMatch = matches.get(0);
			request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.handlerMethod;
		}
		else {
			return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
		}
	}

调用堆栈1

调用堆栈2

4.

初始化HandlerExecutionChain拦截器列表，这个会查找当前容器工厂中所有实现了handleInteropr 的类，

AbstractHandlerMapping类	
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
		HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
				(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
 
		String lookupPath = this.urlPathHelper.getLookupPathForRequest(request, LOOKUP_PATH);
		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;
	}

这个类会根据拦截器的URL匹配规则相应添加拦截器列表。

5.调用所有拦截器的applyPreHandle方法

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = 0; i < interceptors.length; i++) {
				HandlerInterceptor interceptor = interceptors[i];
				if (!interceptor.preHandle(request, response, this.handler)) {
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

7.然后调用invocableMethod.invokeAndHandle(webRequest, mavContainer)，首先通过反射调用handlerMethod中的bean的接口方法

ServletInvocableHandlerMethod
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
 
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);
 
		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				disableContentCachingIfNecessary(webRequest);
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			mavContainer.setRequestHandled(true);
			return;
		}
 
		mavContainer.setRequestHandled(false);
		Assert.state(this.returnValueHandlers != null, "No return value handlers");
		try {
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			if (logger.isTraceEnabled()) {
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

9.最后调用HandlerMethodReturnValueHandlerComposite.handleReturnValue 进行返回值处理，例如将BEAN转JSON,转XML等。

9.1 这个找HANDLER的过程也是，根据此HANDLER是否支持此方法，如在方法上加上了@ResponseBody,则会由RequestResponseBodyMethodProcessor处理。

RequestResponseBodyMethodProcessor
public boolean supportsReturnType(MethodParameter returnType) {
		return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) ||
				returnType.hasMethodAnnotation(ResponseBody.class));
	}

public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
 
		HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
		if (handler == null) {
			throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
		}
		handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
	}

RequestResponseBodyMethodProcessor。
此类继承了AbstractMessageConverterMethodProcessor，这个类会调用当前容器工厂中所有

9.2 由于我们在方法上加了@ResponseBody注解，所有此handler为

protected  void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
			ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
			throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
 
		Object body;
		Class valueType;
		Type targetType;
 
		if (value instanceof CharSequence) {
			body = value.toString();
			valueType = String.class;
			targetType = String.class;
		}
		else {
			body = value;
			valueType = getReturnValueType(body, returnType);
			targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
		}
	
		if (selectedMediaType != null) {
			selectedMediaType = selectedMediaType.removeQualityValue();
			for (HttpMessageConverter converter : this.messageConverters) {
				GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
						(GenericHttpMessageConverter) converter : null);
				if (genericConverter != null ?
						((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
						converter.canWrite(valueType, selectedMediaType)) {
					body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
							(Class>) converter.getClass(),
							inputMessage, outputMessage);
					if (body != null) {
						Object theBody = body;
						LogFormatUtils.traceDebug(logger, traceOn ->
								"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
						addContentDispositionHeader(inputMessage, outputMessage);
						if (genericConverter != null) {
							genericConverter.write(body, targetType, selectedMediaType, outputMessage);
						}
						else {
							((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
						}
					}
					else {
						if (logger.isDebugEnabled()) {
							logger.debug("Nothing to write: null body");
						}
					}
					return;
				}
			}
		}
 
	}

9.3 messageConverts的数据初始化来源为 RequestMappingHandlerAdapter.getDefaultArgumentResolvers方法中，

resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));

messageConverts来源于RequestMappingHandlerAdapter.messageConverters中。

在初始化时会，依赖注入当前系统中所有的messageConvert.

10.最后调用拦截器的所有postHandle方法进行，处理完回调。

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {
 
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = interceptors.length - 1; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				interceptor.postHandle(request, response, this.handler, mv);
			}
		}
	}

11.在渲染完输出视图后，会调用所有拦截器的afterCompletion方法，注意，JSON,XML这种没有视图，只有HTML等才有。

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
			throws Exception {
 
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				try {
					interceptor.afterCompletion(request, response, this.handler, ex);
				}
				catch (Throwable ex2) {
					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
				}
			}
		}
	}

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