org.knopflerfish.util
Class CacheMap

java.lang.Object
  |
  +--java.util.AbstractMap
        |
        +--java.util.HashMap
              |
              +--org.knopflerfish.util.CacheMap

All Implemented Interfaces:

java.lang.Cloneable, java.util.Map, java.io.Serializable

public class CacheMap

extends java.util.HashMap

Timeout version of a HashMap.

Entries in the map have a limited lifelength, and the get method will only return the stored object during a limited time period.

After the timeout period, thr object will be removed.

See Also:

CachedObject, Serialized Form

Inner classes inherited from class java.util.Map

java.util.Map.Entry

Field Summary

protected long

timeout

Constructor Summary

CacheMap()
Create a map with default timeout period.

CacheMap(long timeout)
Create a map with a specified timeout period.

Method Summary

boolean	containsKey(java.lang.Object key) Check if an object exists in the map.
java.lang.Object	get(java.lang.Object key) Get an object from the map.
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Store an object in the map.
void	update() Force timeout check on all items in map and remove all expired keys and objects.

Methods inherited from class java.util.HashMap

clear, clone, containsValue, entrySet, isEmpty, keySet, putAll, remove, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Field Detail

timeout

protected long timeout

Constructor Detail

CacheMap

public CacheMap()

Create a map with default timeout period.

Equivalent to CacheMap(CachedObject.DEFAULT_TIMEOUT)

See Also:

CachedObject.DEFAULT_TIMEOUT, CachedObject

CacheMap

public CacheMap(long timeout)

Create a map with a specified timeout period.

After an object has been stored in the map using put, it will only be available for timeout milliseconds. After that period, get will return null

Parameters:

timeout - timeout period in milliseconds for cached objects.

Method Detail

get

public java.lang.Object get(java.lang.Object key)

Get an object from the map. If the object's timeout period has expired, remove it from the map and return null.

Note: Since the timeout check is done for each cached object, be careful when looping over a map using iterators or other sequences of get. The result from a new get can become null faster than you might think. Thus always check for null return values from get.

Overrides:

get in class java.util.HashMap

containsKey

public boolean containsKey(java.lang.Object key)

Check if an object exists in the map. If non-existent or expired, return false.

Overrides:

containsKey in class java.util.HashMap

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)

Store an object in the map. The object's timeout period will start from the current system time.

Overrides:

put in class java.util.HashMap

update

public void update()

Force timeout check on all items in map and remove all expired keys and objects.

Normally, the timeout check is only done at get calls, but if necessary (for example at periodic complete printouts or before loops) you can (and probably want to) force a timeout check on all cached objects.