springmvc对请求执行流程
doService-->getHandlerMapping-->handlerMapping-->getHandler-->HandlerExecutionChain-->getHandlerAdapter-->
handlerAdapter-->preHandler-->handler-->ModelAndView-->ViewResolver-->view
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doService-->getHandlerMapping-->handlerMapping-->getHandler-->HandlerExecutionChain-->getHandlerAdapter-->
handlerAdapter-->preHandler-->handler-->ModelAndView-->ViewResolver-->view