org.xipki.util

Class LruCache<K,V>

java.lang.Object

org.xipki.util.LruCache<K,V>

public class LruCache<K,V>
extends Object

LRU cache.

Constructor Summary

Constructors

Constructor and Description
LruCache(int maxSize) Constructor with the maximal size.

Method Summary

Modifier and Type	Method and Description
protected V	create(K key) Called after a cache miss to compute a value for the corresponding key.
int	createCount() Returns the number of times create(Object) returned a value.
protected void	entryRemoved(boolean evicted, K key, V oldValue, V newValue) Called for entries that have been evicted or removed.
void	evictAll() Clear the cache, calling entryRemoved(boolean, K, V, V) on each removed entry.
int	evictionCount() Returns the number of values that have been evicted.
V	get(K key) Returns the value for key if it exists in the cache or can be created by #create.
int	hitCount() Returns the number of times get(K) returned a value that was already present in the cache.
Set<K>	keySnapshot() Returns a snapshot of the keys of current cache.
int	maxSize() For caches that do not override sizeOf(K, V), this returns the maximum number of entries in the cache.
int	missCount() Returns the number of times get(K) returned null or required a new value to be created.
V	put(K key, V value) Caches value for key.
int	putCount() Returns the number of times put(K, V) was called.
V	remove(K key) Removes the entry for key if it exists.
void	resize(int maxSize) Sets the size of the cache.
int	size() For caches that do not override sizeOf(K, V), this returns the number of entries in the cache.
protected int	sizeOf(K key, V value) Returns the size of the entry for key and value in user-defined units.
Map<K,V>	snapshot() Returns a snapshot the cache.
String	toString()
void	trimToSize(int maxSize) Remove the eldest entries until the total of remaining entries is at or below the requested size.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

LruCache

public LruCache(int maxSize)

Constructor with the maximal size.

Parameters:

maxSize - for caches that do not override sizeOf(K, V), this is the maximum number of entries in the cache. For all other caches, this is the maximum sum of the sizes of the entries in this cache.

Method Detail

resize

public void resize(int maxSize)

Sets the size of the cache.

Parameters:

maxSize - the new maximum size.

get

public final V get(K key)

Returns the value for key if it exists in the cache or can be created by #create. If a value was returned, it is moved to the head of the queue. This returns null if a value is not cached and could not be created.

Parameters:

key - the key the value for key if it exists in the cache or can be created by #create.

Returns:

the

put

public final V put(K key,
                   V value)

Caches value for key. The value is moved to the head of the queue.

Parameters:

key - the key.

value - the value.

Returns:

the previous value mapped by key.

trimToSize

public void trimToSize(int maxSize)

Remove the eldest entries until the total of remaining entries is at or below the requested size.

Parameters:

maxSize - the maximum size of the cache before returning. Could be -1 to evict even 0-sized elements.

remove

public final V remove(K key)

Removes the entry for key if it exists.

Parameters:

key - the key

Returns:

the previous value mapped by key.

entryRemoved

protected void entryRemoved(boolean evicted,
                            K key,
                            V oldValue,
                            V newValue)

Called for entries that have been evicted or removed. This method is invoked when a value is evicted to make space, removed by a call to remove(K), or replaced by a call to put(K, V). The default implementation does nothing.

The method is called without synchronization: other threads may access the cache while this method is executing.

Parameters:

evicted - true if the entry is being removed to make space, false if the removal was caused by a put(K, V) or remove(K).

key - the key

oldValue - the old value of the key

newValue - the new value for key, if it exists. If non-null, this removal was caused by a put(K, V). Otherwise it was caused by an eviction or a remove(K).

create

protected V create(K key)

Called after a cache miss to compute a value for the corresponding key. Returns the computed value or null if no value can be computed. The default implementation returns null.

The method is called without synchronization: other threads may access the cache while this method is executing.

If a value for key exists in the cache when this method returns, the created value will be released with entryRemoved(boolean, K, V, V) and discarded. This can occur when multiple threads request the same key at the same time (causing multiple values to be created), or when one thread calls put(K, V) while another is creating a value for the same key.

Parameters:

key - the key

Returns:

the created computed value or null if no value can be computed

sizeOf

protected int sizeOf(K key,
                     V value)

Returns the size of the entry for key and value in user-defined units. The default implementation returns 1 so that size is the number of entries and max size is the maximum number of entries.

An entry's size may not change while it is in the cache.

Parameters:

key - the key

value - the value

Returns:

he size of the entry for key and value in user-defined units

evictAll

public final void evictAll()

Clear the cache, calling entryRemoved(boolean, K, V, V) on each removed entry.

size

public final int size()

For caches that do not override sizeOf(K, V), this returns the number of entries in the cache. For all other caches, this returns the sum of the sizes of the entries in this cache.

Returns:

the size

maxSize

public final int maxSize()

For caches that do not override sizeOf(K, V), this returns the maximum number of entries in the cache. For all other caches, this returns the maximum sum of the sizes of the entries in this cache.

Returns:

the maximal size

hitCount

public final int hitCount()

Returns the number of times get(K) returned a value that was already present in the cache.

Returns:

the number of times

missCount

public final int missCount()

Returns the number of times get(K) returned null or required a new value to be created.

Returns:

the number of times returned null or required a new value to be created

createCount

public final int createCount()

Returns the number of times create(Object) returned a value.

Returns:

the number of times create(Object) returned a value.

putCount

public final int putCount()

Returns the number of times put(K, V) was called.

Returns:

the number of times put(K, V) was called.

evictionCount

public final int evictionCount()

Returns the number of values that have been evicted.

Returns:

the number of values that have been evicted.

snapshot

public final Map<K,V> snapshot()

Returns a snapshot the cache.

Returns:

a copy of the current contents of the cache, ordered from least recently accessed to most recently accessed.

keySnapshot

public final Set<K> keySnapshot()

Returns a snapshot of the keys of current cache.

Returns:

a copy of the keys of the current contents of the cache.

toString

public final String toString()

Overrides:

toString in class Object