apollo-demo/src/main/java/com/ctrip/framework/apollo/demo/api/SimpleApolloConfigDemo.java/SimpleApolloConfigDemo/getConfig
class SimpleApolloConfigDemo:  private String getConfig(String key) {
    String result = config.getProperty(key, DEFAULT_VALUE);
    logger.info(String.format("Loading key : %s with value: %s", key, result));
    return result;
  }