Spring MVC从HandlerMapping中获取Handler

        我们常用的@Controller和@RequestMapping注解对应的HandlerMapping类是RequestMappingHandlerMapping，其继承的AbstractHandlerMethodMapping类中缓存了URL到HandlerMethod的映射信息，从RequestMappingHandlerMapping中获取的Handler实际上是HandlerMethod。源码解析如下：

        HandlerMapping的getHandler()方法由抽象类AbstractHandlerMapping实现：

	@Override
	@Nullable
	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        //根据request获取handler，此处handler是HandlerMethod
		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);
		}
        //获取执行链
		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
		if (CorsUtils.isCorsRequest(request)) {
			CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
			CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
			CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
			executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
		}
		return executionChain;
	}

        AbstractHandlerMethodMapping中getHandlerInternal()方法具体实现：

	@Override
	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
		//获取path，从request获取contextPath+RequestUri+RemainingPath
        String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
		if (logger.isDebugEnabled()) {
			logger.debug("Looking up handler method for path " + lookupPath);
		}
        //加读锁
		this.mappingRegistry.acquireReadLock();
		try {
            //根据path找HandlerMethod，从mappingRegistry.urlLookup()中根据url找到
            //对应的List
            //遍历RequestMappingInfo，RequestMappingInfo中有各种condition，根据        
            //request看各个RequestMappingInfo与request是否匹配，匹配的话构造一个新
            //的RequestMappingInfo返回，根据新构造的RequestMappingInfo和
            //从MappingRegistry.getMappings中根据request获取的HandlerMethod，
            //构造Match对象，并加入到List中。
			HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
			if (logger.isDebugEnabled()) {
				if (handlerMethod != null) {
					logger.debug("Returning handler method [" + handlerMethod + "]");
				}
				else {
					logger.debug("Did not find handler method for [" + lookupPath + "]");
				}
			}
			return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
		}
		finally {
            //释放锁
			this.mappingRegistry.releaseReadLock();
		}
	}