@VisibleForTesting
  static boolean isValidJavaClass(String className) {
    for (String part : Splitter.on('.').split(className)) {
      if (!SourceVersion.isIdentifier(part)) {
        return false;
      }
    }
    return true;
  }
Checks if a string is a valid Java class name.

@param className the class name to check
@return {@code true} if {@code className} is a valid Java class name; {@code false} otherwise
jib-plugins-common/src/main/java/com/google/cloud/tools/jib/plugins/common/MainClassResolver.java