org.zkoss.util
Class CacheMap<K,V>

java.lang.Object
  extended by org.zkoss.util.CacheMap<K,V>
All Implemented Interfaces:
java.io.Serializable, java.lang.Cloneable, java.util.Map<K,V>, Cache<K,V>
Direct Known Subclasses:
ResourceCache

public class CacheMap<K,V>
extends java.lang.Object
implements java.util.Map<K,V>, Cache<K,V>, java.io.Serializable, java.lang.Cloneable

The cache map. The key-to-value mappings hold in this map is temporary. They are removed when GC demanding memory and a criteria is met. The criteria is whether the mapping is old enough (called lifetime), or the upper bound is hit (called max-size).

The criteria can be changed by overriding canExpunge(int, org.zkoss.util.CacheMap.Value). When to check the criteria can be changed by overriding shallExpunge().

If the criteria is totally independent of GC, you could override shallExpunge() to always return true (rather than when GC is activated).

It is different from WeakHashMap:

Like other maps, it is not thread-safe. To get one, use java.util.Collections.synchronizedMap.

Implementation Note: there is another version of CacheMap that uses WeakReference for each value (refer to obsolete). The drawback is that all mapping will be queued and need to be examined, because GC tends to release all reference at once.

We don't use PhantomReference because it is still required to re-create the reference after enqueued.

Author:
tomyeh
See Also:
Serialized Form

Nested Class Summary
protected static class CacheMap.Value<V>
          The class to hold key/value.
 
Field Summary
protected static int EXPUNGE_CONTINUE
          Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall continue.
protected static int EXPUNGE_NO
          Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote it shall not be expunged.
protected static int EXPUNGE_STOP
          Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall stop.
protected static int EXPUNGE_YES
          Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote it shall be expunged.
 
Fields inherited from interface org.zkoss.util.Cache
DEFAULT_LIFETIME, DEFAULT_MAX_SIZE
 
Constructor Summary
CacheMap()
          Constructs a cache map.
CacheMap(boolean accessOrder)
          Constructs a cache map.
CacheMap(int cap)
          Constructs a cache map.
CacheMap(int cap, float load)
          Constructs a cache map.
CacheMap(int cap, float load, boolean accessOrder)
          Constructs a cache map.
CacheMap(int maxSize, int lifetime)
          Constructs a cache map with the specified max size and lifetime.
CacheMap(int maxSize, int lifetime, boolean accessOrder)
          Constructs a cache map with the specified max size and lifetime.
 
Method Summary
protected  int canExpunge(int size, CacheMap.Value<V> v)
          Tests whether certain value is OK to expunge.
 void clear()
          Clears all objects being cached.
 java.lang.Object clone()
           
 boolean containsKey(java.lang.Object key)
          Returns whether the specified key is stored.
 boolean containsKeyWithoutExpunge(java.lang.Object key)
          Tests if the given key exists without trying to expunge for more memory.
 boolean containsValue(java.lang.Object value)
           
 java.util.Set<java.util.Map.Entry<K,V>> entrySet()
           
 boolean equals(java.lang.Object o)
           
 int expunge()
          Enforces to expunge items that exceeds the maximal allowed number or lifetime.
 V get(java.lang.Object key)
          Returns the object of the specified key, or null if not found.
 int getLifetime()
          Gets the minimal lifetime, unit=milliseconds.
 int getMaxSize()
          Gets the maximal allowed size.
 V getWithoutExpunge(java.lang.Object key)
          Returns the value without trying to expunge for more memory.
 int hashCode()
           
 boolean isEmpty()
           
 boolean isEmptyWithoutExpunge()
          Returns whether it is empty without trying to expunge first.
 java.util.Set<K> keySet()
           
protected  void onExpunge(CacheMap.Value<V> v)
          Called when a pair of key and value having been expunged.
 V put(K key, V value)
          Stores an object to the cache.
 void putAll(java.util.Map<? extends K,? extends V> map)
           
 V remove(java.lang.Object key)
          Removes an object from the cache.
 void setLifetime(int lifetime)
          Sets the minimal lifetime.
 void setMaxSize(int maxsize)
          Sets the maximal allowed size.
protected  boolean shallExpunge()
          Returns whether it is time to expunge.
 int size()
           
 int sizeWithoutExpunge()
          Returns the size without trying to expunge first.
 java.lang.String toString()
           
 java.util.Collection<V> values()
           
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

EXPUNGE_NO

protected static final int EXPUNGE_NO
Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote it shall not be expunged.

See Also:
Constant Field Values

EXPUNGE_YES

protected static final int EXPUNGE_YES
Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote it shall be expunged.

See Also:
Constant Field Values

EXPUNGE_CONTINUE

protected static final int EXPUNGE_CONTINUE
Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall continue.

See Also:
Constant Field Values

EXPUNGE_STOP

protected static final int EXPUNGE_STOP
Returns by canExpunge(int, org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall stop.

See Also:
Constant Field Values
Constructor Detail

CacheMap

public CacheMap(int maxSize,
                int lifetime)
Constructs a cache map with the specified max size and lifetime. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().

Since:
3.0.0

CacheMap

public CacheMap()
Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().


CacheMap

public CacheMap(int cap)
Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().


CacheMap

public CacheMap(int cap,
                float load)
Constructs a cache map. Unlike LinkedHashMap, the default order is the access order, i.e., the order is changed once accessed, including get().


CacheMap

public CacheMap(boolean accessOrder)
Constructs a cache map.

Parameters:
accessOrder - whether to use the access order. Specify false for the insertion order.
Since:
6.0.0

CacheMap

public CacheMap(int maxSize,
                int lifetime,
                boolean accessOrder)
Constructs a cache map with the specified max size and lifetime.

Parameters:
accessOrder - whether to use the access order. Specify false for the insertion order.
Since:
6.0.0

CacheMap

public CacheMap(int cap,
                float load,
                boolean accessOrder)
Constructs a cache map.

Parameters:
accessOrder - whether to use the access order. Specify false for the insertion order.
Since:
6.0.0
Method Detail

onExpunge

protected void onExpunge(CacheMap.Value<V> v)
Called when a pair of key and value having been expunged. This method is called after it is removed, so you could add it back.

Default: does nothing


shallExpunge

protected boolean shallExpunge()
Returns whether it is time to expunge. Once shallExpunge returns true, values are examined one-by-one thru canExpunge(int, org.zkoss.util.CacheMap.Value), and expunged if EXPUNGE_YES.

This implementation returns true only if GC was activated. You might override it to return true, such that expunge is enforced no matter GC was activated.

See Also:
canExpunge(int, org.zkoss.util.CacheMap.Value)

canExpunge

protected int canExpunge(int size,
                         CacheMap.Value<V> v)
Tests whether certain value is OK to expunge.

Note: values are tested thru canExpunge(int, org.zkoss.util.CacheMap.Value) only if shallExpunge() returns true.

Deriving classes might override this method to return different value for different criteria.

The return value could be a combination of EXPUNGE_xxx. One of EXPUNGE_YES and EXPUNGE_NO is returned to denote whether to expunge the mapping. One of EXPUNGE_CONTINUE and EXPUNGE_STOP is returned to denote whether to continue the searching of the next mapping for expunging.

Normally, you return either (EXPUNGE_YES|EXPUNGE_CONTINUE) or (EXPUNG_NO|EXPUNGE_STOP). Notice that the mapping is queried in the last-access order. Thus, you rarely needs to return (EXPUNGE_NO|EXPUNGE_CONTINUE) unless the appropriate one might be out of this order.

This implementation compares the access time and size. It returns (EXPUNGE_YES|EXPUNGE_CONTINUE) if OK, and (EXPUNGE_NO|EXPUNGE_STOP) if not.

Parameters:
size - the current size. It is used instead of size(), since the entry might not be removed yet (such as FastReadCache).
Returns:
a combination of EXPUNGE_xxx
See Also:
shallExpunge()

expunge

public int expunge()
Enforces to expunge items that exceeds the maximal allowed number or lifetime.

By default, this method is called only GC takes places.

Returns:
number of items left (size()) after expunged
Since:
3.6.1

getLifetime

public int getLifetime()
Gets the minimal lifetime, unit=milliseconds. An mapping won't be removed by GC unless the minimal lifetime or the maximal allowed size exceeds.

Specified by:
getLifetime in interface Cache<K,V>
See Also:
getMaxSize()

setLifetime

public void setLifetime(int lifetime)
Sets the minimal lifetime. Default: Cache.DEFAULT_LIFETIME.

Specified by:
setLifetime in interface Cache<K,V>
Parameters:
lifetime - the lifetime, unit=milliseconds; if non-positive, they will be removed immediately.
See Also:
getLifetime()

getMaxSize

public int getMaxSize()
Gets the maximal allowed size. Default: Cache.DEFAULT_MAX_SIZE. An mapping won't be removed by GC unless the minimal lifetime or the maximal allowed size exceeds.

Notice: getMaxSize() is only a soft limit. It takes effect only if GC takes place.

Specified by:
getMaxSize in interface Cache<K,V>
See Also:
getLifetime()

setMaxSize

public void setMaxSize(int maxsize)
Sets the maximal allowed size.

Specified by:
setMaxSize in interface Cache<K,V>
See Also:
getMaxSize()

isEmpty

public boolean isEmpty()
Specified by:
isEmpty in interface java.util.Map<K,V>

isEmptyWithoutExpunge

public boolean isEmptyWithoutExpunge()
Returns whether it is empty without trying to expunge first.

Since:
3.0.1

size

public int size()
Specified by:
size in interface java.util.Map<K,V>

sizeWithoutExpunge

public int sizeWithoutExpunge()
Returns the size without trying to expunge first.

Since:
3.0.1

clear

public void clear()
Description copied from interface: Cache
Clears all objects being cached.

Specified by:
clear in interface java.util.Map<K,V>
Specified by:
clear in interface Cache<K,V>

remove

public V remove(java.lang.Object key)
Description copied from interface: Cache
Removes an object from the cache.

Specified by:
remove in interface java.util.Map<K,V>
Specified by:
remove in interface Cache<K,V>
Returns:
the object if found.

get

public V get(java.lang.Object key)
Description copied from interface: Cache
Returns the object of the specified key, or null if not found.

Specified by:
get in interface java.util.Map<K,V>
Specified by:
get in interface Cache<K,V>

getWithoutExpunge

public V getWithoutExpunge(java.lang.Object key)
Returns the value without trying to expunge for more memory. It is useful if you want to preserve all entries.


containsKey

public boolean containsKey(java.lang.Object key)
Description copied from interface: Cache
Returns whether the specified key is stored.

Specified by:
containsKey in interface java.util.Map<K,V>
Specified by:
containsKey in interface Cache<K,V>

containsKeyWithoutExpunge

public boolean containsKeyWithoutExpunge(java.lang.Object key)
Tests if the given key exists without trying to expunge for more memory.


containsValue

public boolean containsValue(java.lang.Object value)
Specified by:
containsValue in interface java.util.Map<K,V>

put

public V put(K key,
             V value)
Description copied from interface: Cache
Stores an object to the cache.

Specified by:
put in interface java.util.Map<K,V>
Specified by:
put in interface Cache<K,V>
Returns:
the previous value of the same, or null if no such value

putAll

public void putAll(java.util.Map<? extends K,? extends V> map)
Specified by:
putAll in interface java.util.Map<K,V>

entrySet

public java.util.Set<java.util.Map.Entry<K,V>> entrySet()
Specified by:
entrySet in interface java.util.Map<K,V>

keySet

public java.util.Set<K> keySet()
Specified by:
keySet in interface java.util.Map<K,V>

values

public java.util.Collection<V> values()
Specified by:
values in interface java.util.Map<K,V>

hashCode

public int hashCode()
Specified by:
hashCode in interface java.util.Map<K,V>
Overrides:
hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object o)
Specified by:
equals in interface java.util.Map<K,V>
Overrides:
equals in class java.lang.Object

toString

public java.lang.String toString()
Overrides:
toString in class java.lang.Object

clone

public java.lang.Object clone()
Overrides:
clone in class java.lang.Object


Copyright © 2005-2011 Potix Corporation. All Rights Reserved. SourceForge.net Logo