code: public Map<String, Object> readIfUpdated() throws IOException
      {
          long nowTime = getNowTime();
          if ((nowTime - this.lastWatchTime) <= this.watchInterval)
          {
              return null;
          }
  
          this.lastWatchTime = nowTime;
  
          if (this.targetFile.exists() == false)
          {
              return null;
          }
  
          long targetFileModified = this.targetFile.lastModified();
          if (this.lastModifytime >= targetFileModified)
          {
              return null;
          }
  
          this.lastModifytime = targetFileModified;
  
          return StormConfigGenerator.readYaml(this.targetFile);
      }
docs: Read config file if fulfill following conditions.<br>
  <ol>
  <li>{@literal (nowtime - lastWatchTime) > watchInterval}</li>
  <li>{@literal (target file's lastmodifytime) > lastModifytime}</li>
  </ol>
  
  @return config read result if updated.
  @throws IOException If read failed.