Package org.jivesoftware.util.cache

Class DefaultCache<K extends Serializable,​V extends Serializable>

  • All Implemented Interfaces:
    Map<K,​V>, Cache<K,​V>
    public class DefaultCache<K extends Serializable,​V extends Serializable>
extends Object
implements Cache<K,​V>
    Default, non-distributed implementation of the Cache interface. The algorithm for cache is as follows: a HashMap is maintained for fast object lookup. Two linked lists are maintained: one keeps objects in the order they are accessed from cache, the other keeps objects in the order they were originally added to cache. When objects are added to cache, they are first wrapped by a CacheObject which maintains the following pieces of information:
    • The size of the object (in bytes).
    • A pointer to the node in the linked list that maintains accessed order for the object. Keeping a reference to the node lets us avoid linear scans of the linked list.
    • A pointer to the node in the linked list that maintains the age of the object in cache. Keeping a reference to the node lets us avoid linear scans of the linked list.

    To get an object from cache, a hash lookup is performed to get a reference to the CacheObject that wraps the real object we are looking for. The object is subsequently moved to the front of the accessed linked list and any necessary cache cleanups are performed. Cache deletion and expiration is performed as needed.

    Author:
    Matt Tucker

    • Field Detail

      • map

        protected Map<K extends Serializable,​org.jivesoftware.util.cache.DefaultCache.CacheObject<V extends Serializable>> map
        The map the keys and values are stored in.

    • Method Detail

      • getName

        public String getName()
        Returns the name of this cache. The name is completely arbitrary and used only for display to administrators.
        Specified by:
        getName in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the name of this cache.

      • getCacheHits

        public long getCacheHits()
        Returns the number of cache hits. A cache hit occurs every time the get method is called and the cache contains the requested object.

        Keeping track of cache hits and misses lets one measure how efficient the cache is; the higher the percentage of hits, the more efficient.

        Specified by:
        getCacheHits in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the number of cache hits.

      • getCacheMisses

        public long getCacheMisses()
        Returns the number of cache misses. A cache miss occurs every time the get method is called and the cache does not contain the requested object.

        Keeping track of cache hits and misses lets one measure how efficient the cache is; the higher the percentage of hits, the more efficient.

        Specified by:
        getCacheMisses in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the number of cache hits.

      • getCacheSize

        public int getCacheSize()
        Returns the size of the cache contents in bytes. This value is only a rough approximation, so cache users should expect that actual VM memory used by the cache could be significantly higher than the value reported by this method.
        Specified by:
        getCacheSize in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the size of the cache contents in bytes.

      • getMaxCacheSize

        public long getMaxCacheSize()
        Returns the maximum size of the cache (in bytes). If the cache grows larger than the max size, the least frequently used items will be removed. If the max cache size is set to -1, there is no size limit.
        Specified by:
        getMaxCacheSize in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the maximum size of the cache (-1 indicates unlimited max size).

      • setMaxCacheSize

        public void setMaxCacheSize​(int maxCacheSize)
        Sets the maximum size of the cache. If the cache grows larger than the max size, the least frequently used items will be removed. If the max cache size is set to -1, there is no size limit.
        Specified by:
        setMaxCacheSize in interface Cache<K extends Serializable,​V extends Serializable>
        Parameters:
        maxCacheSize - the maximum size of this cache (-1 indicates unlimited max size).

      • getMaxLifetime

        public long getMaxLifetime()
        Returns the maximum number of milliseconds that any object can live in cache. Once the specified number of milliseconds passes, the object will be automatically expired from cache. If the max lifetime is set to -1, then objects never expire.
        Specified by:
        getMaxLifetime in interface Cache<K extends Serializable,​V extends Serializable>
        Returns:
        the maximum number of milliseconds before objects are expired.

      • setMaxLifetime

        public void setMaxLifetime​(long maxLifetime)
        Sets the maximum number of milliseconds that any object can live in cache. Once the specified number of milliseconds passes, the object will be automatically expired from cache. If the max lifetime is set to -1, then objects never expire.
        Specified by:
        setMaxLifetime in interface Cache<K extends Serializable,​V extends Serializable>
        Parameters:
        maxLifetime - the maximum number of milliseconds before objects are expired.

      • getCacheCulls

        public long getCacheCulls​(Duration duration)