code: private static Class checkClass(ProtoFile protoFile, Type type, Map<String, String> mappedUniName,
              boolean isUniName) {
          String packageName = protoFile.getPackageName();
          String defaultClsName = type.getName();
          // to check if has "java_package" option and "java_outer_classname"
          List<Option> options = protoFile.getOptions();
          if (options != null) {
              for (Option option : options) {
                  if (option.getName().equals(JAVA_PACKAGE_OPTION)) {
                      packageName = option.getValue().toString();
                  } else if (option.getName().equals(JAVA_OUTER_CLASSNAME_OPTION)) {
                      defaultClsName = option.getValue().toString();
                  }
              }
          }
  
          String simpleName = getProxyClassName(defaultClsName, mappedUniName, isUniName);
          String className = packageName + PACKAGE_SPLIT_CHAR + simpleName;
  
          Class<?> c = null;
          try {
              c = Class.forName(className);
          } catch (ClassNotFoundException e1) {
              // if class not found so should generate a new java source class.
              c = null;
          }
  
          return c;
      }
docs: Check class.
  
  @param protoFile the proto file
  @param type the type
  @param mappedUniName the mapped uni name
  @param isUniName the is uni name
  @return the class