HashMap with weak values

Question

I\'m implementing a cache for Objects stored persistently. The idea is:

• Method getObjectFromPersistence(long id); ///Takes about 3 seconds
• M

Answer 1

You can use the Guava MapMaker for this:

ConcurrentMap graphs = new MapMaker()
   .weakValues()
   .makeMap();

You can even include the computation part by replacing makeMap() with this:

   .makeComputingMap(
       new Function() {
         public CustomObject apply(Long id) {
           return getObjectFromPersistence(id);
         }
       });

Since what you are writing looks a lot like a cache, the newer, more specialized Cache (built via a CacheBuilder) might be even more relevant to you. It doesn't implement the Map interface directly, but provides even more controls that you might want for a cache.

You can refer to this for a detailed how to work for CacheBuilder and here is an example for fast access:

LoadingCache cache = CacheBuilder.newBuilder()
   .maximumSize(100)
   .expireAfterWrite(10, TimeUnit.MINUTES)
   .build(
       new CacheLoader() {
           @Override
           public String load(Integer id) throws Exception {
               return "value";
           }
       }
   );