apollo-client/src/main/java/com/ctrip/framework/apollo/internals/ConfigServiceLocator.java/ConfigServiceLocator/getDeprecatedCustomizedConfigService
class ConfigServiceLocator:  @SuppressWarnings("deprecation")
  private String getDeprecatedCustomizedConfigService() {
    // 1. Get from System Property
    String configServices = System.getProperty(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE);
    if (!Strings.isNullOrEmpty(configServices)) {
      DeprecatedPropertyNotifyUtil.warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE,
          ApolloClientSystemConsts.APOLLO_CONFIG_SERVICE);
    }
    if (Strings.isNullOrEmpty(configServices)) {
      // 2. Get from OS environment variable
      configServices = System.getenv(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE_ENVIRONMENT_VARIABLES);
      if (!Strings.isNullOrEmpty(configServices)) {
        DeprecatedPropertyNotifyUtil.warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE_ENVIRONMENT_VARIABLES,
            ApolloClientSystemConsts.APOLLO_CONFIG_SERVICE_ENVIRONMENT_VARIABLES);
      }
    }
    if (Strings.isNullOrEmpty(configServices)) {
      // 3. Get from server.properties
      configServices = Foundation.server().getProperty(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE, null);
      if (!Strings.isNullOrEmpty(configServices)) {
        DeprecatedPropertyNotifyUtil.warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_CONFIG_SERVICE,
            ApolloClientSystemConsts.APOLLO_CONFIG_SERVICE);
      }
    }
    return configServices;
  }