Package com.sun.identity.entitlement.opensso

Class Cache

java.lang.Object

java.util.Dictionary

com.sun.identity.entitlement.opensso.Cache

All Implemented Interfaces:

Map

public class Cache
extends Dictionary
implements Map

IMPORTANT NOTE: The cache has be implemented by modifing the existing java.util.Hashtable code. Its has added functionality of a built in replacement strategy which in this case is based on Least Recently Used concept. The synchronization functionality that exists in a Hashtable has been removed to improve performance.

The class Cache provides the functionality to cache objects based on their usage. The maximum size of the cache can be set using the constructor. If the maximum size is not set the default cache size for Cache will be obtained from the config file ??? file, defined using the key ???. The object that needs to be cached can be supplied to the instance of this class using the put method. The object can be obtained by invoking the get method on the instance. Each object that is cached is tracked based on its usage. If a new object needs to added to the cache and the maximum size limit of the cache is reached, then the least recently used object is replaced. This class implements a Cache, which maps keys to values. Any non-null object can be used as a key or as a value.

To successfully store and retrieve objects from a Cache, the objects used as keys must implement the hashCode method and the equals method.

An instance of Cache has three parameters that affect its performance: initial capacity, maximum size and load factor. The maximum capacity is the maximum number of buckets in the hash table, and the initial capacity is simply the capacity at the time the hash table is created. Note that the hash table is open: in the case a "hash collision", a single bucket stores multiple entries, which must be searched sequentially. The load factor is a measure of how full the hash table is allowed to get before its capacity is automatically increased. When the number of entries in the Cache exceeds the product of the load factor and the current capacity, the capacity is increased by calling the rehash method.

Generally, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values decrease the space overhead but increase the time cost to look up an entry (which is reflected in most Cache operations, including get and put).

The capacity controls a tradeoff between wasted space and the need for rehash operations, which are time-consuming. No rehash operations will ever occur if the capacity is greater than the maximum number of entries the Cache will contain divided by its load factor. However, setting the capacity too high can waste space.

If many entries are to be made into a Cache, creating it with a sufficiently large capacity may allow the entries to be inserted more efficiently than letting it perform automatic rehashing as needed to grow the table.

This class has been retrofitted to implement Map, so that it becomes a part of Java's collection framework. The Iterators returned by the iterator and listIterator methods of the Collections returned by all of Cache's "collection view methods" are fail-fast: if the Cache is structurally modified at any time after the Iterator is created, in any way except through the Iterator's own remove or add methods, the Iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the Iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. The Enumerations returned by Cache's keys and values methods are not fail-fast.

Since:

JDK1.0

See Also:

Object.equals(java.lang.Object), Object.hashCode(), Collection, Map

Constructor Summary

Constructors

Constructor	Description
Cache()
Cache(String name, int initCapacity, int maxSize)	Constructs a new, empty Cache with the specified capacity and default load factor, which is 0.75.
Cache(String name, int initCapacity, int maxSize, float loadFactor)	Constructs a new, empty Cache with the specified capacity and the specified load factor.

Method Summary

Modifier and Type	Method	Description
protected void	adjustEntry(Object key)	This method adjusts the table by removing the entry corresponding to key from the table.
String	audit()
void	clear()	Clears this Cache so that it contains no keys.
boolean	contains(Object value)	Tests if some key maps into the specified value in this Cache.
boolean	containsKey(Object key)	Tests if the specified object is a key in this Cache.
boolean	containsValue(Object value)	Returns true if this Cache maps one or more keys to this value.
Enumeration	elements()	Returns an enumeration of the values in this Cache.
Set	entrySet()	Returns a Set view of the entries contained in this Cache.
boolean	equals(Object o)	Compares the specified Object with this Map for equality, as per the definition in the Map interface.
Object	get(Object key)	Returns the value to which the specified key is mapped in this Cache.
String	getName()	Returns name.
int	hashCode()	Returns the hash code value for this Map as per the definition in the Map interface.
boolean	isEmpty()	Tests if this Cache maps no keys to values.
Enumeration	keys()	Returns an enumeration of the keys in this Cache.
Set	keySet()	Returns a Set view of the keys contained in this Cache.
Object	put(Object key, Object value)	Maps the specified key to the specified value in this Cache.
void	putAll(Map t)	Copies all of the mappings from the specified Map to this Hashtable These mappings will replace any mappings that this Hashtable had for any of the keys currently in the specified Map.
protected void	rehash()	Increases the capacity of and internally reorganizes this Cache, in order to accommodate and access its entries more efficiently.
Object	remove(Object key)	Removes the key (and its corresponding value) from this Cache.
int	size()	Returns the number of keys in this Cache.
String	toString()	Returns a string representation of this Cache object in the form of a set of entries, enclosed in braces and separated by the ASCII characters ", " (comma and space).
Collection	values()	Returns a Collection view of the values contained in this Cache.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

Constructor Detail

Cache

public Cache(String name,
             int initCapacity,
             int maxSize,
             float loadFactor)

Constructs a new, empty Cache with the specified capacity and the specified load factor.

Parameters:

name - Name of cache.

initCapacity - the capacity of the Cache.

maxSize - the maximum size of the cache.

loadFactor - the load factor of the Cache.

Throws:

IllegalArgumentException - if the capacity is less than zero, or if the load factor is nonpositive.

Cache

public Cache(String name,
             int initCapacity,
             int maxSize)

Constructs a new, empty Cache with the specified capacity and default load factor, which is 0.75.

Parameters:

name - Name of cache.

initCapacity - the initial capacity of the Cache.

maxSize - the maximum size of the cache.

Throws:

IllegalArgumentException - if the capacity is less than zero.

Cache

public Cache()

Method Detail

getName

public String getName()

Returns name.

Returns:

name.

size

public int size()

Returns the number of keys in this Cache.

Specified by:

size in interface Map

Specified by:

size in class Dictionary

Returns:

the number of keys in this Cache.

isEmpty

public boolean isEmpty()

Tests if this Cache maps no keys to values.

Specified by:

isEmpty in interface Map

Specified by:

isEmpty in class Dictionary

Returns:

true if this Cache maps no keys to values; false otherwise.

keys

public Enumeration keys()

Returns an enumeration of the keys in this Cache.

Specified by:

keys in class Dictionary

Returns:

an enumeration of the keys in this Cache.

See Also:

Enumeration, elements(), keySet(), Map

elements

public Enumeration elements()

Returns an enumeration of the values in this Cache. Use the Enumeration methods on the returned object to fetch the elements sequentially.

Specified by:

elements in class Dictionary

Returns:

an enumeration of the values in this Cache.

See Also:

Enumeration, keys(), values(), Map

contains

public boolean contains(Object value)

Tests if some key maps into the specified value in this Cache. This operation is more expensive than the containsKey method.

Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the PolicyCollections framework).

Parameters:

value - a value to search for.

Returns:

true if and only if some key maps to the value argument in this Cache as determined by the equals method; false otherwise.

Throws:

NullPointerException - if the value is null.

See Also:

containsKey(Object), containsValue(Object), Map

containsValue

public boolean containsValue(Object value)

Returns true if this Cache maps one or more keys to this value.

Note that this method is identical in functionality to contains (which predates the Map interface).

Specified by:

containsValue in interface Map

Parameters:

value - value whose presence in this Cache is to be tested.

Since:

JDK1.2

See Also:

Map

containsKey

public boolean containsKey(Object key)

Tests if the specified object is a key in this Cache.

Specified by:

containsKey in interface Map

Parameters:

key - possible key.

Returns:

true if and only if the specified object is a key in this Cache, as determined by the equals method; false otherwise.

See Also:

contains(Object)

get

public Object get(Object key)

Returns the value to which the specified key is mapped in this Cache.

Specified by:

get in interface Map

Specified by:

get in class Dictionary

Parameters:

key - a key in the Cache.

Returns:

the value to which the key is mapped in this Cache; null if the key is not mapped to any value in this Cache.

See Also:

put(Object, Object)

rehash

protected void rehash()

Increases the capacity of and internally reorganizes this Cache, in order to accommodate and access its entries more efficiently. This method is called automatically when the number of keys in the Cache exceeds this Cache's capacity and load factor. It ensures the new capacity does not exceed the maximum size.

put

public Object put(Object key,
                  Object value)

Maps the specified key to the specified value in this Cache. Neither the key nor the value can be null. If the cache is full to its capacity, then the least recently used entry in the cache will be replaced.

The value can be retrieved by calling the get method with a key that is equal to the original key.

Specified by:

put in interface Map

Specified by:

put in class Dictionary

Parameters:

key - the Cache key.

value - the value.

Returns:

the previous value of the specified key in this Cache, or null if it did not have one.

Throws:

NullPointerException - if the key or value is null.

See Also:

Object.equals(Object), get(Object)

adjustEntry

protected void adjustEntry(Object key)

This method adjusts the table by removing the entry corresponding to key from the table.

remove

public Object remove(Object key)

Removes the key (and its corresponding value) from this Cache. This method does nothing if the key is not in the Cache.

Specified by:

remove in interface Map

Specified by:

remove in class Dictionary

Parameters:

key - the key that needs to be removed.

Returns:

the value to which the key had been mapped in this Cache, or null if the key did not have a mapping.

putAll

public void putAll(Map t)

Copies all of the mappings from the specified Map to this Hashtable These mappings will replace any mappings that this Hashtable had for any of the keys currently in the specified Map.

Specified by:

putAll in interface Map

Since:

JDK1.2

clear

public void clear()

Clears this Cache so that it contains no keys.

Specified by:

clear in interface Map

toString

public String toString()

Returns a string representation of this Cache object in the form of a set of entries, enclosed in braces and separated by the ASCII characters ", " (comma and space). Each entry is rendered as the key, an equals sign =, and the associated element, where the toString method is used to convert the key and element to strings.

Overrides to toString method of Object.

Overrides:

toString in class Object

Returns:

a string representation of this Cache.

audit

public String audit()

keySet

public Set keySet()

Returns a Set view of the keys contained in this Cache. The Set is backed by the Cache, so changes to the Cache are reflected in the Set, and vice-versa. The Set supports element removal (which removes the corresponding entry from the Cache), but not element addition.

Specified by:

keySet in interface Map

Since:

JDK1.2

entrySet

public Set entrySet()

Returns a Set view of the entries contained in this Cache. Each element in this collection is a Map.Entry. The Set is backed by the Cache, so changes to the Cache are reflected in the Set, and vice-versa. The Set supports element removal (which removes the corresponding entry from the Cache), but not element addition.

Specified by:

entrySet in interface Map

Since:

JDK1.2

See Also:

Map.Entry

values

public Collection values()

Returns a Collection view of the values contained in this Cache. The Collection is backed by the Cache, so changes to the Cache are reflected in the Collection, and vice-versa. The Collection supports element removal (which removes the corresponding entry from the Cache), but not element addition.

Specified by:

values in interface Map

Since:

JDK1.2

equals

public boolean equals(Object o)

Compares the specified Object with this Map for equality, as per the definition in the Map interface.

Specified by:

equals in interface Map

Overrides:

equals in class Object

Returns:

true if the specified Object is equal to this Map.

Since:

JDK1.2

See Also:

Map.equals(Object)

hashCode

public int hashCode()

Returns the hash code value for this Map as per the definition in the Map interface.

Specified by:

hashCode in interface Map

Overrides:

hashCode in class Object

Since:

JDK1.2

See Also:

Map.hashCode()