apollo-client/src/main/java/com/ctrip/framework/apollo/internals/PropertiesConfigFile.java/PropertiesConfigFile/doGetContent
class PropertiesConfigFile:  String doGetContent() {
    if (!this.hasContent()) {
      return null;
    }

    try {
      return PropertiesUtil.toString(m_configProperties.get());
    } catch (Throwable ex) {
      ApolloConfigException exception =
          new ApolloConfigException(String
              .format("Parse properties file content failed for namespace: %s, cause: %s",
                  m_namespace, ExceptionUtil.getDetailMessage(ex)));
      Tracer.logError(exception);
      throw exception;
    }
  }