SpringMVC 6+源码分析（三）DispatcherServlet实例化流程 2--（url 与contrller类如何进行映射）

一、概述

上一章了解了DispatcherServlet初始化的流程，着重讲了一个重点的初始化业务，本章节将重点讲解项目中的 controller 怎么跟url经行关联的。这一关键的业务流程都在 initHandlerMappings(context) 方法中完成的。

二、初始化处理器映射器-initHandlerMappings

initHandlerMappings初始化是SpringMVC中请求映射的核心链路，包括HandlerMapping的注入和HandlerMethod的注册。从Spring启动时加载HandlerMapping到解析请求路径找到相应的Controller方法，深入探讨了SpringMVC处理HTTP请求的内部机制。

	private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> 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) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}

		for (HandlerMapping mapping : this.handlerMappings) {
			if (mapping.usesPathPatterns()) {
				this.parseRequestPath = true;
				break;
			}
		}
	}

从方法中我们可以看到，在这个过程中会先去Spring容器中查找是否存在自定义的HandlerMapping 的bean，存在则加入handlerMappings。如果没有则加载默认配置的HandlerMapping，默认的HandlerMapping实现类使用资源加载的方式。对应的实现类在配置文件 DispatcherServlet.properties 中，通过资源加载器，获取到默认HandlerMapping的类信息。

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

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

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
	org.springframework.web.servlet.function.support.HandlerFunctionAdapter


org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
	org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
	org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

可以看到系统默认加载的HandlerMapping 有 BeanNameUrlHandlerMapping、RequestMappingHandlerMapping、RouterFunctionMapping。在日常的业务开发中，业务处理都是在RequestMappingHandlerMapping中的，所以重点看RequestMappingHandlerMapping的实例化过程即可。

RequestMappingHandlerMapping继承 AbstractHandlerMethodMapping、AbstractHandlerMapping 而它们还要实现InitializingBean接口，所以RequestMappingHandlerMapping对象被容器创建之后，就会调用afterPropertiesSet()方法进行初始化。

	@Override
	@SuppressWarnings("deprecation")
	public void afterPropertiesSet() {
		this.config = new RequestMappingInfo.BuilderConfiguration();
		this.config.setTrailingSlashMatch(useTrailingSlashMatch());
		this.config.setContentNegotiationManager(getContentNegotiationManager());

		if (getPatternParser() != null && this.defaultPatternParser &&
				(this.useSuffixPatternMatch || this.useRegisteredSuffixPatternMatch)) {

			setPatternParser(null);
		}

		if (getPatternParser() != null) {
			this.config.setPatternParser(getPatternParser());
			Assert.isTrue(!this.useSuffixPatternMatch && !this.useRegisteredSuffixPatternMatch,
					"Suffix pattern matching not supported with PathPatternParser.");
		}
		else {
			this.config.setSuffixPatternMatch(useSuffixPatternMatch());
			this.config.setRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch());
			this.config.setPathMatcher(getPathMatcher());
		}

		super.afterPropertiesSet();
	}

在容器创建完对象以后，调用RequestMappingHandlerMapping的 afterPropertiesSet方法，这里做了RequestMappingInfo.BuilderConfiguration的初始化，然后调用AbstractHandlerMethodMapping的afterPropertiesSet方法。

	@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());
	}

这里开始遍历IOC容器中的bean，并经行下一步的处理。

	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);
		}
	}

	@Override
	protected boolean isHandler(Class<?> beanType) {
		return AnnotatedElementUtils.hasAnnotation(beanType, Controller.class);
	}

判断bean是否存在 Controller 注解，如果存在则对该bean进行处理。在此方法中开始遍历bean中的方法。

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

		if (handlerType != null) {
			Class<?> userType = ClassUtils.getUserClass(handlerType);
			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));
			}
			else if (mappingsLogger.isDebugEnabled()) {
				mappingsLogger.debug(formatMappings(userType, methods));
			}
			methods.forEach((method, mapping) -> {
				Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
				registerHandlerMethod(handler, invocableMethod, mapping);
			});
		}
	}

先判断方法上是否存在 RequestMapping注解如果存在则开始 创建RequestMappingInfo实例，将注解中的 url path 转成视图可识别的格式保存（并将controller 上的 path 值拼接上去），同时保存各类参数。

@Override
	@Nullable
	protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
		RequestMappingInfo info = createRequestMappingInfo(method);
		if (info != null) {
			RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
			if (typeInfo != null) {
				info = typeInfo.combine(info);
			}
			if (info.isEmptyMapping()) {
				info = info.mutate().paths("", "/").options(this.config).build();
			}
			String prefix = getPathPrefix(handlerType);
			if (prefix != null) {
				info = RequestMappingInfo.paths(prefix).options(this.config).build().combine(info);
			}
		}
		return info;
	}

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

	protected RequestMappingInfo createRequestMappingInfo(
			RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition) {

		RequestMappingInfo.Builder builder = RequestMappingInfo
				.paths(resolveEmbeddedValuesInPatterns(requestMapping.path()))
				.methods(requestMapping.method())
				.params(requestMapping.params())
				.headers(requestMapping.headers())
				.consumes(requestMapping.consumes())
				.produces(requestMapping.produces())
				.mappingName(requestMapping.name());
		if (customCondition != null) {
			builder.customCondition(customCondition);
		}
		return builder.options(this.config).build();
	}

每个方法都会生成对应的 RequestMappingInfo，之后开始注册到MappingRegistry 对象中。

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

	public void register(T mapping, Object handler, Method method) {
			this.readWriteLock.writeLock().lock();
			try {
				HandlerMethod handlerMethod = createHandlerMethod(handler, method);
				validateMethodMapping(handlerMethod, mapping);

				Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
				for (String path : directPaths) {
					this.pathLookup.add(path, mapping);
				}

				String name = null;
				if (getNamingStrategy() != null) {
					name = getNamingStrategy().getName(handlerMethod, mapping);
					addMappingName(name, handlerMethod);
				}

				CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
				if (corsConfig != null) {
					corsConfig.validateAllowCredentials();
					corsConfig.validateAllowPrivateNetwork();
					this.corsLookup.put(handlerMethod, corsConfig);
				}

				this.registry.put(mapping,
						new MappingRegistration<>(mapping, handlerMethod, directPaths, name, corsConfig != null));
			}
			finally {
				this.readWriteLock.writeLock().unlock();
			}
		}

在register方法中，先根据 对象及方法 创建HandlerMethod对象，再判断mapping是否已经存在，如果存在则抛出对应的错误。后续开始对mapping进行处理。
首先将路径映射到快速索引中，this.pathLookup，主要的作用是 通过path 快速找到对应的 RequestMappingInfo从而找到 对应的方法，
如：
“/api/getUser/info” -> getUserInfo() 方法。
同时支持 支持路径模式匹配
例如：
“/api/getUserByid/7234” 它可以匹配到
“/api/getUserByid/{id }” 或者 “/api/getUserByid/*” 等url。
pathLookup由于使用 MultiValueMap 结构，同一个路径模式可关联多个 RequestMappingInfo 对象
这对路径的动态参数匹配至关重要。

接下来是将注定nameLookup，nameLookup是一个映射，键（key）是处理器方法的名字（通常是方法名或用户指定的名称），值（value）是该名称对应的HandlerMethod列表。在RequestMapping 中设置类name 属性，则将name 作为key，如果没有设置则使用自定义策略生成对应的key，框架在获取不到指定策略时，将使用默认的策略生成 name 作为key，默认策略是 使用类名+“#” +方法名的 方式。

protected RequestMappingInfoHandlerMapping() {
		setHandlerMethodMappingNamingStrategy(new RequestMappingInfoHandlerMethodMappingNamingStrategy());
	}

@Override
	public String getName(HandlerMethod handlerMethod, RequestMappingInfo mapping) {
		if (mapping.getName() != null) {
			return mapping.getName();
		}
		StringBuilder sb = new StringBuilder();
		String simpleTypeName = handlerMethod.getBeanType().getSimpleName();
		for (int i = 0; i < simpleTypeName.length(); i++) {
			if (Character.isUpperCase(simpleTypeName.charAt(i))) {
				sb.append(simpleTypeName.charAt(i));
			}
		}
		sb.append(SEPARATOR).append(handlerMethod.getMethod().getName());
		return sb.toString();
	}

nameLookup 其主要作用是通过处理器方法名称快速查找对应的 HandlerMethod 对象。

接下来就是将跨域配置注册到this.corsLookup属性类中。

		CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
				if (corsConfig != null) {
					corsConfig.validateAllowCredentials();
					corsConfig.validateAllowPrivateNetwork();
					this.corsLookup.put(handlerMethod, corsConfig);
				}

最后将 映射关系 添加在registry 中，将 RequestMappingInfo作为值，MappingRegistration对象作为value，用于存储所有控制器方法（HandlerMethod）与请求映射条件（如 URL 模式、HTTP 方法等）的绑定关系。为后续的执行流程提供映射表。

三、结尾

至此 url 与contrller类的映射主流程就基本完成，下一章节将介绍 adapter的初始化，及Springmvc的执行流程。在此过程中如存在纰漏或者错误，麻烦请支持，相互探讨相互学习。