SpringMVC：RequestMappingHandlerMapping初始化源码阅读。

喜欢ヅ旅行 2022-01-28 15:01 263阅读 0赞

首先，我们在AnnotationDrivenBeanDefinitionParser中会实例化一个RequestMappingHandlerMapping实例，然后向Spring容器中注册这个实例。

查看其父类可知，实现了InitializingBean接口。所以在实例化后会调用afterPropertiesSet方法

public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean

由此可见这个方法是用来在实例化时探测handler方法

/**
    	 * Detects handler methods at initialization.
    	 */
    	@Override
    	public void afterPropertiesSet() {
    		initHandlerMethods();
    	}

扫描ApplicationContext中的bean,探测和注册handler method

/**
    	 * Scan beans in the ApplicationContext, detect and register handler methods.
    	 * @see #isHandler(Class)
    	 * @see #getMappingForMethod(Method, Class)
    	 * @see #handlerMethodsInitialized(Map)
    	 */
    	protected void initHandlerMethods() {
    		if (logger.isDebugEnabled()) {
    			logger.debug("Looking for request mappings in application context: " + getApplicationContext());
    		}
    //...根据BeanFactory中存放的Bean的类型，找到所有的注册Bean
    		String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
    				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
    				getApplicationContext().getBeanNamesForType(Object.class));
    
    		for (String beanName : beanNames) {
    //根据RequestMapping或者Controller注解判断是不是Handler
    			if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX) &&
    					isHandler(getApplicationContext().getType(beanName))){
    				detectHandlerMethods(beanName);//探测
    			}
    		}
    		handlerMethodsInitialized(getHandlerMethods());
    	}

根据Method上的RequestMapping注解查找一个Handler中的handler方法

/**
    	 * 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) ?//判定是不是字符串，是则根据根据字符串获得其对应的类名
    				getApplicationContext().getType((String) handler) : handler.getClass();
     
    		final Class<?> userType = ClassUtils.getUserClass(handlerType);//判定是不是自定义的
                    //根据一个方法过滤器获得被RequestMapping注解标记的Method
    		Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
    			public boolean matches(Method method) {
    				return getMappingForMethod(method, userType) != null;
    			}
    		});
     
    		for (Method method : methods) {遍历这个method集合，所以可知，每一个Method都会有对应的MappingInfo与之对应
    			T mapping = getMappingForMethod(method, userType);//根据Method和类获取MappingInfo
                            //将返回的RequestMappingInfo注册到RequestMappingHandlerMapping上
                            registerHandlerMethod(handler, method, mapping);
    		}
    	}

使用方法和类级别的注解去创建一个RequestMappingInfo

protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
    		RequestMappingInfo info = null;//寻找方法上的RequestMapping注解，返回RequestMapping注解
    		RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);
    		if (methodAnnotation != null) {
    			RequestCondition<?> methodCondition = getCustomMethodCondition(method);//一个空的实现
    			info = createRequestMappingInfo(methodAnnotation, methodCondition);//创建一个RequestMappingInfo
    			RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);
    			if (typeAnnotation != null) {//虚招类上的RequestMapping注解，如果有，则进行组合操作
    				RequestCondition<?> typeCondition = getCustomTypeCondition(handlerType);//空的实现
    				info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);//组合MethodInfo
    			}
    		}
    		return info;//返回这个RequestMappingInfo
    	}

需要详细对RequestMappingInfo这个类进行分析，特别是其combine方法和里面的几个重要的属性。

protected RequestMappingInfo createRequestMappingInfo(RequestMapping annotation,
    			RequestCondition<?> customCondition) {
     
    		String[] patterns = resolveEmbeddedValuesInPatterns(annotation.value());
    		return new RequestMappingInfo(
    				new PatternsRequestCondition(patterns, getUrlPathHelper(), getPathMatcher(),
    					this.useSuffixPatternMatch, this.useTrailingSlashMatch, this.fileExtensions),
    				new RequestMethodsRequestCondition(annotation.method()),
    				new ParamsRequestCondition(annotation.params()),
    				new HeadersRequestCondition(annotation.headers()),
    				new ConsumesRequestCondition(annotation.consumes(), annotation.headers()),
    				new ProducesRequestCondition(annotation.produces(), annotation.headers(),
                                             getContentNegotiationManager()),
    				customCondition);
    	}

将返回的RequestMappingInfo注册到RequestMappingHandlerMapping上,其中两个重要的属性handlerMethods以及urlMap。使用HandlerMethod是可以理解的，因为在调用Method时肯定需要传入一个instance实例才行，而handler则对应这个实例。所以将这两个封装在一个对象里，方便传递。

protected void registerHandlerMethod(Object handler, Method method, T mapping) {
    		HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);//方法内部直接new出一个HandlerMethod对象
                    //handlerMethods用来存放RequestMappingInfo与HandlerMethod的键值对  ，         
                    HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);
                    //如果本来就已经存在不相同的HandlerMethod则抛出异常
                    if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
    			throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean()
    					+ "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '"
    					+ oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
    		}
                    //将RequestMappingInfo与HandlerMethod放入handlerMethods属性中
    		this.handlerMethods.put(mapping, newHandlerMethod);
    		if (logger.isInfoEnabled()) {
    			logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);
    		}
                    //从RequestMappingInfo中获得一个pattern集合，就是ReqeustMapping注解的value值。。
    		Set<String> patterns = getMappingPathPatterns(mapping);
    		for (String pattern : patterns) {
    			if (!getPathMatcher().isPattern(pattern)) {
                    //将这个pattern与RequestMappingInfo关联起来，以便以后根据url进行匹配找到MappingInfo,再根据MappingInfo找到HandlerMethod
                                 this.urlMap.add(pattern, mapping);
    			}
    		}
    	}

至此可以知道初始化RequestMappingHandlerMapping时是将所有用ReqeustMapping标记的类和方法包装在一个HandlerMethod中，然后将其与RequestMappingInfo进行配对，并存入RequestMappingHandlerMapping的handlerMethods中。将pattern与RequestMappingInfo进行配对，存入RequestMappingHandlerMapping的urlMap中。可以预测，在servlet提供服务时，会根据requestPath匹配对应的url，进而得到HandlerMethod，处理具体业务。

转载：[https://blog.csdn.net/u013828625/article/details/80360000][https_blog.csdn.net_u013828625_article_details_80360000]

[https_blog.csdn.net_u013828625_article_details_80360000]: https://blog.csdn.net/u013828625/article/details/80360000