Caffeine Cache - Specify expiry for an entry

user_703139 0
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I'm trying to further my understanding of the caffeine cache. I was wondering if there is a way to specify a timeout for an entry that's populated in the cache, but have no time based expiry for the rest of the records.

Essentially I would like to have the following interface:

put(key, value, timeToExpiry)// enter a key and value with a specified timeToExpiry

put(key, value) // enter a key value with no timeToExpiry

I can write the interfaces and plumbing, but I'd like to understand how I can configure caffeine for both of the above requirements. I'm also open to have two separate instances of the caffeine cache.

caffeine java
1 Answers

This can be done by using a custom expiration policy and leverage an unreachable duration. The maximum duration is Long.MAX_VALUE, which is 292 years in nanoseconds. Assuming your record holds when (and if) it expires then you might configure the cache as,

LoadingCache<Key, Graph> graphs = Caffeine.newBuilder()
    .expireAfter(new Expiry<Key, Graph>() {
      public long expireAfterCreate(Key key, Graph graph, long currentTime) {
        if (graph.getExpiresOn() == null) {
          return Long.MAX_VALUE;
        }
        long seconds = graph.getExpiresOn()
            .minus(System.currentTimeMillis(), MILLIS)
            .toEpochSecond();
        return TimeUnit.SECONDS.toNanos(seconds);
      }
      public long expireAfterUpdate(Key key, Graph graph, 
          long currentTime, long currentDuration) {
        return currentDuration;
      }
      public long expireAfterRead(Key key, Graph graph,
          long currentTime, long currentDuration) {
        return currentDuration;
      }
    })
    .build(key -> createExpensiveGraph(key));
Ben_194500
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