code: protected String resolveJarFile() {
          Class resourceClass = resourceInfo.getResourceClass();
          if (resourceClass == null) return null;
          String classFile = resourceClass.getName().replace(".", "/") + ".class";
          URL classUrl = IOUtils.getResource(classFile);
          String urlProtocol = classUrl.getProtocol();
          if (urlProtocol.equals("jar")) {
              String path = classUrl.getPath();
              return path.substring(0, path.length() - classFile.length() - 1);
          }
          return null;
      }
docs: <p>resolveJarFile.</p>
  
  @return a {@link java.lang.String} object.