apollo-client/src/main/java/com/ctrip/framework/apollo/internals/AbstractConfig.java/AbstractConfig/getBooleanProperty
class AbstractConfig:  @Override
  public Boolean getBooleanProperty(String key, Boolean defaultValue) {
    try {
      if (m_booleanCache == null) {
        synchronized (this) {
          if (m_booleanCache == null) {
            m_booleanCache = newCache();
          }
        }
      }

      return getValueFromCache(key, Functions.TO_BOOLEAN_FUNCTION, m_booleanCache, defaultValue);
    } catch (Throwable ex) {
      Tracer.logError(new ApolloConfigException(
          String.format("getBooleanProperty for %s failed, return default value %b", key,
              defaultValue), ex));
    }
    return defaultValue;
  }