springMVC源码探索之RequestMappingHandlerMapping

RequestMappingHandlerMapping

• 简介
• 方法
• • detectHandlerMethods
  • afterPropertiesSet
  • isHandler
  • getMappingForMethod
  • createRequestMappingInfo

简介

RequestMappingHandlerMapping是AbstractHandlerMethodMapping 抽象类的唯一实现类，它的作用 是根据在Controller中的@RequestMapping注解生成RequestMappingInfo。

方法

上一篇在记录AbstractHandlerMethodMapping源码是有出现过一些方法，AbstractHandlerMethodMapping是抽象类这些方法的具体实现都在子类RequestMappingHandlerMapping 中。

detectHandlerMethods

AbstractHandlerMethodMapping#detectHandlerMethods() 这个方法的作用是从handler中获取handler method并注册。detectHandlerMethods 有些方法是需要RequestMappingHandlerMapping 实现的，相关方法会在下面介绍。

/**
	 * Look for handler methods in a handler.
	 * @param handler the bean name of a handler or a handler instance
	 */
	protected void detectHandlerMethods(final Object handler) {
		Class<?> handlerType = (handler instanceof String ?
				obtainApplicationContext().getType((String) handler) : handler.getClass());

		if (handlerType != null) {
			//为给定的类返回用户定义的类:通常只是给定的类，如果是cglib生成的子类，则返回原始的类。
			final Class<?> userType = ClassUtils.getUserClass(handlerType);
			Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
					(MethodIntrospector.MetadataLookup<T>) method -> {
						try {
							// 为处理程序方法提供映射
							return getMappingForMethod(method, userType);
						}
						catch (Throwable ex) {
							throw new IllegalStateException("Invalid mapping on handler class [" +
									userType.getName() + "]: " + method, ex);
						}
					});
			if (logger.isDebugEnabled()) {
				logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
			}

			// 为查找到的handler method 进行注册
			methods.forEach((method, mapping) -> {
				Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
				registerHandlerMethod(handler, invocableMethod, mapping);
			});
		}
	}

afterPropertiesSet

初始化bean是调用的方法，各种配置设置并调用父类afterPropertiesSet 方法。

@Override
	public void afterPropertiesSet() {
	// 各种配置设置
		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());
		// 调用AbstractHandlerMethodMapping afterPropertiesSet 方法
		super.afterPropertiesSet();
	}

isHandler

isHandler 方法作用是判断提供的handler是否有@Controller或@RequestMapping注解

/**
	 * {@inheritDoc}
	 * <p>Expects a handler to have either a type-level @{@link Controller}
	 * annotation or a type-level @{@link RequestMapping} annotation.
	 */
	@Override
	protected boolean isHandler(Class<?> beanType) {
		return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
				AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
	}

getMappingForMethod

通过@RequestMapping 注解生成一个RequestMappingInfo 对象并返回，如果没有使用RequestMapping 注解会返回null，主要还是看createRequestMappingInfo 方法

@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);
			}
		}
		return info;
	}

createRequestMappingInfo

createRequestMappingInfo 解析RequestMapping 注解 生成RequestMappingInfo对象。
createRequestMappingInfo(AnnotatedElement element)这个方法会先判断参数类型，然后根据类型去查找是否有额外的请求条件，如果有就把条件RequestMapping 和 条件做为参数调用重载方法
createRequestMappingInfo(RequestMapping requestMapping, @Nullable RequestCondition<?> customCondition);

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

getCustomTypeCondition和getCustomMethodCondition 这两个方法没有实现，它们的作用是自定义请求参数条件，如果需要可以继承AbstractRequestCondition 和使用CompositeRequestCondition 类来提供多个自定义条件。

重载方法createRequestMappingInfo，实际生成RequestMappingInfo 的方法，

/**
	 * Create a {@link RequestMappingInfo} from the supplied
	 * {@link RequestMapping @RequestMapping} annotation, which is either
	 * a directly declared annotation, a meta-annotation, or the synthesized
	 * result of merging annotation attributes within an annotation hierarchy.
	 */
	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();
	}

上面就是简单的介绍了一下springmvc路径映射过程，有兴趣的还是看下源码吧，
能力有限，水平一般，如有错误，请多指出。