public String getString(final String key, final String defaultValue) {
    if (containsKey(key)) {
      return get(key);
    } else {
      return defaultValue;
    }
  }
Gets the string from the Props. If it doesn't exist, it will return the defaultValue
dss-appconn/appconns/dss-eventchecker-appconn/src/main/java/com/webank/wedatasphere/dss/appconn/eventchecker/utils/Props.java