apollo-client/src/main/java/com/ctrip/framework/apollo/internals/AbstractConfig.java/AbstractConfig/getValueFromCache
class AbstractConfig:  private <T> T getValueFromCache(String key, Function<String, T> parser, Cache<String, T> cache, T defaultValue) {
    T result = cache.getIfPresent(key);

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

    return getValueAndStoreToCache(key, parser, cache, defaultValue);
  }