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## org.jivesoftware.util.cache
Class DefaultCache<K,V>

    java.lang.Object
      org.jivesoftware.util.cache.DefaultCache<K,V>

All Implemented Interfaces:
  Map<K,V>, Cache<K,V>

    public class DefaultCache<K,V>

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

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map
`Map.Entry<K,V>`

Field Summary
`protected LinkedList` | `ageList` Linked list to maintain time that cache objects were initially added to the cache, most recently added to oldest added.
`protected long` | `cacheHits` Maintain the number of cache hits and misses.
`protected long` | `cacheMisses` Maintain the number of cache hits and misses.
`protected LinkedList` | `lastAccessedList` Linked list to maintain order that cache objects are accessed in, most used to least used.
`protected Map<K,org.jivesoftware.util.cache.DefaultCache.CacheObject<V>>` | `map` The map the keys and values are stored in.
`protected long` | `maxLifetime` Maximum length of time objects can exist in cache before expiring.

Constructor Summary
`DefaultCache(String name, long maxSize, long maxLifetime)` Create a new default cache and specify the maximum size of for the cache in bytes, and the maximum lifetime of objects.

Method Summary
`void` | `clear()`
`boolean` | `containsKey(Object key)`
`boolean` | `containsValue(Object value)`
`protected void` | `cullCache()` Removes objects from cache if the cache is too full.
`protected void` | `deleteExpiredEntries()` Clears all entries out of cache where the entries are older than the maximum defined age.
`Set<Map.Entry<K,V>>` | `entrySet()`
`V` | `get(Object key)`
`long` | `getCacheHits()` Returns the number of cache hits.
`long` | `getCacheMisses()` Returns the number of cache misses.
`int` | `getCacheSize()` Returns the size of the cache contents in bytes.
`long` | `getMaxCacheSize()` Returns the maximum size of the cache (in bytes).
`long` | `getMaxLifetime()` Returns the maximum number of milleseconds that any object can live in cache.
`String` | `getName()` Returns the name of this cache.
`boolean` | `isEmpty()`
`Set<K>` | `keySet()`
`V` | `put(K key, V value)`
`void` | `putAll(Map<? extends K,? extends V> map)`
`V` | `remove(Object key)`
`void` | `setMaxCacheSize(int maxCacheSize)` Sets the maximum size of the cache.
`void` | `setMaxLifetime(long maxLifetime)` Sets the maximum number of milleseconds that any object can live in cache.
`void` | `setName(String name)` Sets the name of this cache.
`int` | `size()`
`Collection<V>` | `values()`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Methods inherited from interface java.util.Map
`equals, hashCode`

Field Detail

### map

    protected Map<K,org.jivesoftware.util.cache.DefaultCache.CacheObject<V>> map

  The map the keys and values are stored in.

### lastAccessedList

    protected LinkedList lastAccessedList

  Linked list to maintain order that cache objects are accessed in, most used to least used.

### ageList

    protected LinkedList ageList

  Linked list to maintain time that cache objects were initially added to the cache, most recently added to oldest added.

### maxLifetime

    protected long maxLifetime

  Maximum length of time objects can exist in cache before expiring.

### cacheHits

    protected long cacheHits

  Maintain the number of cache hits and misses. A cache hit occurs every time the get method is called and the cache contains the requested object. A cache miss represents the opposite occurence.

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

### cacheMisses

    protected long cacheMisses

  Maintain the number of cache hits and misses. A cache hit occurs every time the get method is called and the cache contains the requested object. A cache miss represents the opposite occurence.

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

Constructor Detail

### DefaultCache

    public DefaultCache(String name,
                        long maxSize,
                        long maxLifetime)

  Create a new default cache and specify the maximum size of for the cache in bytes, and the maximum lifetime of objects.

  Parameters:
    `name` - a name for the cache.
    `maxSize` - the maximum size of the cache in bytes. -1 means the cache has no max size.
    `maxLifetime` - the maximum amount of time objects can exist in cache before being deleted. -1 means objects never expire.

Method Detail

### put

    public V put(K key,
                 V value)

  Specified by:
    `put` in interface `Map<K,V>`

### get

    public V get(Object key)

  Specified by:
    `get` in interface `Map<K,V>`

### remove

    public V remove(Object key)

  Specified by:
    `remove` in interface `Map<K,V>`

### clear

    public void clear()

  Specified by:
    `clear` in interface `Map<K,V>`

### size

    public int size()

  Specified by:
    `size` in interface `Map<K,V>`

### isEmpty

    public boolean isEmpty()

  Specified by:
    `isEmpty` in interface `Map<K,V>`

### values

    public Collection<V> values()

  Specified by:
    `values` in interface `Map<K,V>`

### containsKey

    public boolean containsKey(Object key)

  Specified by:
    `containsKey` in interface `Map<K,V>`

### putAll

    public void putAll(Map<? extends K,? extends V> map)

  Specified by:
    `putAll` in interface `Map<K,V>`

### containsValue

    public boolean containsValue(Object value)

  Specified by:
    `containsValue` in interface `Map<K,V>`

### entrySet

    public Set<Map.Entry<K,V>> entrySet()

  Specified by:
    `entrySet` in interface `Map<K,V>`

### keySet

    public Set<K> keySet()

  Specified by:
    `keySet` in interface `Map<K,V>`

### 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,V>`
  Returns:
    the name of this cache.

### setName

    public void setName(String name)

  Sets the name of this cache.

  Specified by:
    `setName` in interface `Cache<K,V>`
  Parameters:
    `name` - 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,V>`
  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,V>`
  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,V>`
  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,V>`
  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,V>`
  Parameters:
    `maxCacheSize` - the maximum size of this cache (-1 indicates unlimited max size).

### getMaxLifetime

    public long getMaxLifetime()

  Returns the maximum number of milleseconds that any object can live in cache. Once the specified number of milleseconds passes, the object will be automatically expried from cache. If the max lifetime is set to -1, then objects never expire.

  Specified by:
    `getMaxLifetime` in interface `Cache<K,V>`
  Returns:
    the maximum number of milleseconds before objects are expired.

### setMaxLifetime

    public void setMaxLifetime(long maxLifetime)

  Sets the maximum number of milleseconds that any object can live in cache. Once the specified number of milleseconds passes, the object will be automatically expried from cache. If the max lifetime is set to -1, then objects never expire.

  Specified by:
    `setMaxLifetime` in interface `Cache<K,V>`
  Parameters:
    `maxLifetime` - the maximum number of milleseconds before objects are expired.

### deleteExpiredEntries

    protected void deleteExpiredEntries()

  Clears all entries out of cache where the entries are older than the maximum defined age.

### cullCache

    protected final void cullCache()

  Removes objects from cache if the cache is too full. "Too full" is defined as within 3% of the maximum cache size. Whenever the cache is is too big, the least frequently used elements are deleted until the cache is at least 10% empty.

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