code: public static File toJsonFile(String jsonString, File returnJsonFile) {
          try {
              jsonMapper.writeValue(returnJsonFile, jsonString);
              return returnJsonFile;
          } catch (Exception e) {
              return JMExceptionManager.handleExceptionAndReturnNull(log, e,
                      "toJsonFile", jsonString);
          }
      }
docs: To json file file.
  
  @param jsonString     the json string
  @param returnJsonFile the return json file
  @return the file