Guava cache: how to set expiration on 'CacheLoader.load()' instead of during CacheBuilder.newBuilder()?

Question

I am trying to create a cache using guava cache library. One my main requirement is that I want to set the cache expiry after the CacheLoader.load(..) function instead of something most of the examples I encountered on the web, like the one below.

LoadingCache<String, MyClass> myCache = 
CacheBuilder.newBuilder().maximumSize(MAX_SIZE).expireAfterWrite(10, TimeUnit.Minutes).build(cacheLoader);

The reason for this is that the object retrieved from the database by the CacheLoader.load(...) function contains the expiration data. So I want to use this information instead of some "random" static value.

I want something like this.

LoadingCache<String, MyClass> myCache = 
CacheBuilder.newBuilder().maximumSize(MAX_SIZE).build(cacheLoader);

...

CacheLoader meCacheLoder = new CacheLoader<String MyClass>(){
   @Override
   public MyClass load(String key) throws Exception {
      // Retrieve the MyClass object from database using 'key'
      MyClass myObj = getMyObjectFromDb(key);  
      int expiry = myObj.getExpiry();

         // Now somehow set this 'expiry' value with the cache
         ????

      return myObj;
   }
 };

OR Is there any better option available than Guava cache for this purpose?

Answer 1

There is no such feature in Guava, as Louis already pointed out.

For example you can use EHCache or cache2k . For cache2k I can give you quick directions since this is a core feature we use regularly:

You can either implement the interface ValueWithExpiryTime on your value object, which is:

interface ValueWithExpiryTime {

  long getCacheExpiryTime();

}

Or, you can register a EntryExpiryCalculator to extract the time value. The cache is build as follows:

Cache<Key, Value> cache = 
  CacheBuilder.newCache(Key.class, Value.class)
    .expiryCalculator(new EntryExpiryCalculator<Key, Value>() {
        @Override
        public long calculateExpiryTime(
            final Key key, final Value value, 
            final long loadTime, final CacheEntry<Key, Value> oldEntry) {
          return value.getExpiry();
        }
      }
    )
    .build();

The time is the standard long type represented in milliseconds since the epoch. By default the expiry will happen not exactly at the specified time, but zero or a few milliseconds later, depending on your machine load. This is the most effective mode. If this is a problem, add sharpExpiry(true) .

Disclaimer: I am the author of cache2k....