apollo-core/src/main/java/com/ctrip/framework/foundation/internals/DefaultProviderManager.java/DefaultProviderManager/getProperty
class DefaultProviderManager:  @Override
  public String getProperty(String name, String defaultValue) {
    for (Provider provider : m_providers.values()) {
      String value = provider.getProperty(name, null);

      if (value != null) {
        return value;
      }
    }

    return defaultValue;
  }