源码跟踪-springmvc(三)：RequestMapping

DispatcherServlet.getHandler

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        if (this.handlerMappings != null) {
            for (HandlerMapping mapping : this.handlerMappings) {
                HandlerExecutionChain handler = mapping.getHandler(request);
                if (handler != null) {
                    return handler;
                }
            }
        }
        return null;
    }

DispatcherServlet.getHandler方法真正调用的其实就是RequestMappingHandlerMapping.getHadler方法，返回的HandlerExecutionChain中有真正的handler和3个拦截器，分别是LongTaskTimingHandlerInterceptor，ConversionServiceExposingInterceptor，ResourceUrlProviderExposingInterceptor。

1. RequestMappingHandlerMapping是怎么通过request定位到对应的handler的
2. RequestMappingHandlerMapping怎么获取到拦截器的，如果我要写个拦截器，应该怎么配置，有什么注意事项

//todo