code: protected URL findResource(Klass c, String fileName) {
          boolean ends = false;
          for (String ext : allowedExtensions) {
              if (fileName.endsWith(ext)) {
                  ends = true;
                  break;
              }
          }
          if (!ends)  return null;
  
          for ( ; c!=null; c=c.getSuperClass()) {
              URL res = c.getResource(fileName);
              if (res!=null)  return res;
          }
          return null;
      }
docs: Determines if this resource can be served