apollo-client/src/main/java/com/ctrip/framework/apollo/util/ConfigUtil.java/ConfigUtil/getPropertyBoolean
class ConfigUtil:  private boolean getPropertyBoolean(String propertyName, String envName, boolean defaultVal) {
    String enablePropertyNamesCache = System.getProperty(propertyName);
    if (Strings.isNullOrEmpty(enablePropertyNamesCache)) {
      enablePropertyNamesCache = System.getenv(envName);
    }
    if (Strings.isNullOrEmpty(enablePropertyNamesCache)) {
      enablePropertyNamesCache = Foundation.app().getProperty(propertyName, null);
    }
    if (!Strings.isNullOrEmpty(enablePropertyNamesCache)) {
      try {
        return Boolean.parseBoolean(enablePropertyNamesCache);
      } catch (Throwable ex) {
        logger.warn("Config for {} is invalid: {}, set default value: {}",
                propertyName, enablePropertyNamesCache, defaultVal);
      }
    }
    return defaultVal;
  }