org.zkoss.util
Class CacheMap

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

public class CacheMap
extends java.lang.Object
implements java.util.Map, Cache, 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(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 newQueue() to return null. Then, shallExpunge() always returns true (rather than when GC is activated) -- of course, you could override shallExpunge(), too.

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
          The class to hold key/value.
 
Field Summary
protected static int EXPUNGE_CONTINUE
          Returns by canExpunge(org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall continue.
protected static int EXPUNGE_NO
          Returns by canExpunge(org.zkoss.util.CacheMap.Value) to denote it shall not be expunged.
protected static int EXPUNGE_STOP
          Returns by canExpunge(org.zkoss.util.CacheMap.Value) to denote the searching of the next mapping shall stop.
protected static int EXPUNGE_YES
          Returns by canExpunge(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 cachemap by using LinkedHashMap internally.
CacheMap(int cap)
          Constructs a cachemap by using LinkedHashMap internally.
CacheMap(int cap, float load)
          Constructs a cachemap by using LinkedHashMap internally.
CacheMap(int maxSize, int lifetime)
          Constructs a cache map with the specified max size and lifetime.
 
Method Summary
protected  int canExpunge(CacheMap.Value v)
          Tests whether certain value is OK to expunge.
 void clear()
          Clears all objects being cached.
 java.lang.Object clone()
          To make sure that it is in the acess order.
 boolean containsKey(java.lang.Object key)
          Returns whether the specified key is stored.
 boolean containsValue(java.lang.Object value)
           
 java.util.Set entrySet()
           
 boolean equals(java.lang.Object o)
           
 int expunge()
          Enforces to expunge items that exceeds the maximal allowed number or lifetime.
 java.lang.Object 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.
 java.lang.Object getWithoutExpunge(java.lang.Object key)
          Returns the value without trying to expunge first.
 int hashCode()
           
 boolean isEmpty()
          Gets the last accessed time, in system millisecs.
 boolean isEmptyWithoutExpunge()
          Returns whether it is empty without trying to expunge first.
 java.util.Set keySet()
           
protected  java.lang.ref.ReferenceQueue newQueue()
          Creates the reference queue.
protected  void onExpunge(CacheMap.Value v)
          Called when a pair of key and value having been expunged.
 java.lang.Object put(java.lang.Object key, java.lang.Object value)
          Stores an object to the cache.
 void putAll(java.util.Map map)
           
 java.lang.Object 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 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(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(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(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(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.

Since:
3.0.0

CacheMap

public CacheMap()
Constructs a cachemap by using LinkedHashMap internally.


CacheMap

public CacheMap(int cap)
Constructs a cachemap by using LinkedHashMap internally.


CacheMap

public CacheMap(int cap,
                float load)
Constructs a cachemap by using LinkedHashMap internally.

Method Detail

onExpunge

protected void onExpunge(CacheMap.Value 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(org.zkoss.util.CacheMap.Value), and expunged if EXPUNGE_YES.

This implementation returns true only if newQueue() returns null (in constructor) or GC was activated. You might override it to enforce expunge besides GC.

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

canExpunge

protected int canExpunge(CacheMap.Value v)
Tests whether certain value is OK to expunge.

Note: values are tested thru canExpunge(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 coulde 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.

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

newQueue

protected java.lang.ref.ReferenceQueue newQueue()
Creates the reference queue. It is called only once in the constructor (so it is meaningless to change the returned value after constructed).

Default: new ReferenceQueue();
Override this method to return null if you want to expunge items every time get(java.lang.Object) or put(java.lang.Object, java.lang.Object) is called -- not only GC is activated. In other words, if newQueue() returns null, shallExpunge() always returns true (unless you override it too).


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
See Also:
getMaxSize()

setLifetime

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

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

getMaxSize

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

Specified by:
getMaxSize in interface Cache
See Also:
getLifetime()

setMaxSize

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

Specified by:
setMaxSize in interface Cache
See Also:
getMaxSize()

isEmpty

public boolean isEmpty()
Gets the last accessed time, in system millisecs.

Specified by:
isEmpty in interface java.util.Map
Returns:
the last accessed time; 0 if not found

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

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
Specified by:
clear in interface Cache

remove

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

Specified by:
remove in interface java.util.Map
Specified by:
remove in interface Cache
Returns:
the object if found.

get

public java.lang.Object 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
Specified by:
get in interface Cache

getWithoutExpunge

public java.lang.Object getWithoutExpunge(java.lang.Object key)
Returns the value without trying to expunge first. 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
Specified by:
containsKey in interface Cache

containsValue

public boolean containsValue(java.lang.Object value)
Specified by:
containsValue in interface java.util.Map

put

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

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

putAll

public void putAll(java.util.Map map)
Specified by:
putAll in interface java.util.Map

entrySet

public java.util.Set entrySet()
Specified by:
entrySet in interface java.util.Map

keySet

public java.util.Set keySet()
Specified by:
keySet in interface java.util.Map

values

public java.util.Collection values()
Specified by:
values in interface java.util.Map

hashCode

public int hashCode()
Specified by:
hashCode in interface java.util.Map
Overrides:
hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object o)
Specified by:
equals in interface java.util.Map
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()
To make sure that it is in the acess order.

Overrides:
clone in class java.lang.Object


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