code: static void preHandleMultipartRequest(HttpServletRequest request)
          throws ServletException
      {
          MultipartRequestHandler multipartHandler = getCachedMultipartHandler(request);
          
          if (multipartHandler == null)
          {
              multipartHandler = getMultipartHandler(request);
              
              if (multipartHandler != null)
              {
                  //
                  // Run the request through the handler, and cache the handler in the outer request.
                  //
                  multipartHandler.handleRequest(request);
                  HttpServletRequest outerRequest = ScopedServletUtils.getOuterRequest(request);
                  outerRequest.setAttribute(PREHANDLED_MULTIPART_REQUEST_ATTR, multipartHandler);
              }
          }
      }
docs: Can be called early in the request processing cycle to cache a single multipart handler for the request.