如何在咖啡因缓存中缓存空值

Question

我正在使用 Caffeine 缓存来存储从外部系统接收的数据。

LoadingCache<String, String> clientCache = Caffeine.newBuilder().expireAfterWrite(1, TimeUnit.MINUTES).build(id -> {
  System.out.println("Generating new value for " + id);
  if (id.equalsIgnoreCase("1")) {
    return null;
  }
  return new Date().toString();
});

System.out.println(clientCache.get("1"));
System.out.println(clientCache.get("1"));
System.out.println(clientCache.get("2"));
System.out.println(clientCache.get("3"));

结果是，

Generating new value for 1
null
Generating new value for 1
null
Generating new value for 2
Wed May 20 17:11:01 IST 2020
Generating new value for 3
Wed May 20 17:11:01 IST 2020
Wed May 20 17:11:01 IST 2020

Caffeine 没有在缓存中保存空值。如何在 Caffeine 中存储空值？

Answer 1

来自this issue report：

The cache does not allow storing null values. If you perform a computation and return null then this indicates the data doesn't exist and the caller receives null.

此外，它建议：

Optional is a good technique for negative caching.

如何在咖啡因缓存中缓存空值

How to cache null values in caffeine cache

java

caffeine

caffeine-cache