上一篇我们简单介绍了注册Mapping ，这次我们介绍怎么查找。首先我们知道Spring mvc的核心组件DispatcherServlet，他是一个Servlet，并且所有的请求都要交给他来处理，
我们看一下他的doService，他里面调用了doDispatch来处理请求

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
         ...
         // Determine handler for the current request.
         mappedHandler = getHandler(processedRequest);   //这就是我们这片文章索要讲述的，获取mappinghander
         ...
}

看一下具体的实现

/**
 * 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);   // 获取Handler
      if (handler != null) {
         return handler;
      }
   }
   return null;
}

@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
   Object handler = getHandlerInternal(request);  //获得内部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);  //解析得到请求的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();
   }
}

上一篇我们将找到，所有的MappingHandler,都放进了mappingRegistry，在这里就发挥了用处，根据url找到具体的
HandlerMethod，然后返回，在org.springframework.web.servlet.handler.AbstractHandlerMapping#getHandler中封装成HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
然后返回executionChain，给DispatchServlet使用。就是这么查的，比较清爽一点