上一篇我們簡單介紹了注冊Mapping ，這次我們介紹怎么查找。首先我們知道Spring mvc的核心組件DispatcherServlet，他是一個Servlet，并且所有的請求都要交給他來處理，
我們看一下他的doService，他里面調用了doDispatch來處理請求

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
         ...
         // Determine handler for the current request.
         mappedHandler = getHandler(processedRequest);   //這就是我們這片文章索要講述的，獲取mappinghander
         ...
}

看一下具體的實現

/**
 * Return the HandlerExecutionChain for this request.
 * <p>Tries all handler mappings in order.
 * @param request current HTTP request
 * @return the HandlerExecutionChain, or {@code null} if no handler could be found
 */
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
   for (HandlerMapping hm : this.handlerMappings) {
      if (logger.isTraceEnabled()) {
         logger.trace(
               "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
      }
      HandlerExecutionChain handler = hm.getHandler(request);   // 獲取Handler
      if (handler != null) {
         return handler;
      }
   }
   return null;
}

@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
   Object handler = getHandlerInternal(request);  //獲得內部handler
   if (handler == null) {
      handler = getDefaultHandler();
   }
   if (handler == null) {
      return null;
   }
   // Bean name or resolved handler?
   if (handler instanceof String) {
      String handlerName = (String) handler;
      handler = getApplicationContext().getBean(handlerName);
   }

   HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
   if (CorsUtils.isCorsRequest(request)) {
      CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
      CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
      CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
      executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
   }
   return executionChain;
}

/**
 * Look up a handler method for the given request.
 */
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
   String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);  //解析得到請求的URL
   if (logger.isDebugEnabled()) {
      logger.debug("Looking up handler method for path " + lookupPath);
   }
   this.mappingRegistry.acquireReadLock();  
   try {
      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 {
      this.mappingRegistry.releaseReadLock();
   }
}

上一篇我們將找到，所有的MappingHandler,都放進了mappingRegistry，在這里就發揮了用處，根據url找到具體的
HandlerMethod，然后返回，在org.springframework.web.servlet.handler.AbstractHandlerMapping#getHandler中封裝成HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
然后返回executionChain，給DispatchServlet使用。就是這么查的，比較清爽一點