code: protected String resolveResourceContextPath(HttpServletRequest request, String resource) {
          final String resourceContextPath = this.getResourceServerContextPath();
          
          this.logger.debug("Attempting to locate resource serving webapp with context path: {}", resourceContextPath);
          
          //Try to resolve the 
          final ServletContext resourceContext = this.servletContext.getContext(resourceContextPath);
          if (resourceContext == null || !resourceContextPath.equals(resourceContext.getContextPath())) {
              this.logger.warn("Could not find resource serving webapp under context path {} ensure the resource server is deployed and cross context dispatching is enable for this web application", resourceContextPath);
              return request.getContextPath();
          }
          
          this.logger.debug("Found resource serving webapp at: {}", resourceContextPath);
          
          URL url = null;
          try {
              url = resourceContext.getResource(resource);
          }
          catch (MalformedURLException e) {
              //Ignore
          }
          
          if (url == null) {
              this.logger.debug("Resource serving webapp {} doesn't contain resource {} Falling back to the local resource.", resourceContextPath, resource);
              return request.getContextPath();
          }
          
          this.logger.debug("Resource serving webapp {} contains resource {} Using resource server.", resourceContextPath, resource);
          return resourceContextPath;
      }
docs: If the resource serving servlet context is available and the resource
  is available in the context, create a URL to the resource in that context.
  If not, create a local URL for the requested resource.