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A Cache is similar to ConcurrentMap, but not quite the same. The most fundamental difference is that a ConcurrentMap persists all elements that are added to it until they are explicitly removed. A
Cache on the other hand is generally configured to evict entries automatically, in order to constrain its memory footprint. In some cases a
AsyncLoadingCache can be useful even if it doesn't evict entries, due to its automatic cache loading.
Caffeine provide flexible construction to create a cache with a combination of the following features:
- automatic loading of entries into the cache, optionally asynchronously
- size-based eviction when a maximum is exceeded based on frequency and recency
- time-based expiration of entries, measured since last access or last write
- asynchronously refresh when the first stale request for an entry occurs
- keys automatically wrapped in weak references
- values automatically wrapped in weak or soft references
- notification of evicted (or otherwise removed) entries
- writes propagated to an external resource
- accumulation of cache access statistics
To improve integration, JSR-107 JCache and Guava adapters are provided in extension modules. JSR-107 standardizes a Java 6 based API to minimize vendor specific code at the cost of features and performance. Guava's Cache is the predecessor library and the adapters provide a simple migration strategy.