net.sourceforge.jtds.jdbc.cache
Class ProcedureCache

java.lang.Object
  net.sourceforge.jtds.jdbc.cache.ProcedureCache

All Implemented Interfaces:

StatementCache

public class ProcedureCache

extends java.lang.Object

implements StatementCache

LRU cache for procedures and statement handles.

Version:

$Id: ProcedureCache.java,v 1.5 2005-07-05 16:44:25 alin_sinpalean Exp $

Nested Class Summary

private static class

ProcedureCache.CacheEntry Encapsulates the cached Object and implements the linked list used to implement the LRU logic.

Field Summary

private java.util.HashMap	cache The actual cache instance.
(package private) int	cacheSize Maximum cache size or 0 to disable.
(package private) java.util.ArrayList	free List of redundant cache entries.
(package private) ProcedureCache.CacheEntry	head Head node of the linked list.
private static int	MAX_INITIAL_SIZE The maximum initial HashMap size.
(package private) ProcedureCache.CacheEntry	tail Tail node of the linked list.

Constructor Summary

ProcedureCache(int cacheSize)
Constructs a new statement cache.

Method Summary

java.lang.Object	get(java.lang.String key) Retrieves a ProcEntry object from the cache.
java.util.Collection	getObsoleteHandles(java.util.Collection handles) Obtains a list of statement handles or procedures that can now be dropped.
void	put(java.lang.String key, java.lang.Object handle) Inserts a new entry, identified by a key, into the cache.
void	remove(java.lang.String key) Removes a redundant entry from the cache.
private void	scavengeCache() Removes unused entries trying to bring down the cache to the requested size.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_INITIAL_SIZE

private static final int MAX_INITIAL_SIZE

The maximum initial HashMap size.

See Also:

Constant Field Values

cache

private java.util.HashMap cache

The actual cache instance.

cacheSize

int cacheSize

Maximum cache size or 0 to disable.

head

ProcedureCache.CacheEntry head

Head node of the linked list.

tail

ProcedureCache.CacheEntry tail

Tail node of the linked list.

free

java.util.ArrayList free

List of redundant cache entries.

Constructor Detail

ProcedureCache

public ProcedureCache(int cacheSize)

Constructs a new statement cache.

Parameters:

cacheSize - maximum cache size or 0 to disable caching

Method Detail

get

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

Retrieves a ProcEntry object from the cache.

If the entry exists it is moved to the front of the linked list to keep it alive as long as possible.

Specified by:

get in interface StatementCache

Parameters:

key - the key value identifying the required entry

Returns:

the keyed entry as an Object or null if the entry does not exist

put

public void put(java.lang.String key,
                java.lang.Object handle)

Inserts a new entry, identified by a key, into the cache.

If the cache is full then one or more entries are removed and transferred to a list for later destruction.

Specified by:

put in interface StatementCache

Parameters:

key - value used to identify the entry

handle - proc entry to be inserted into the cache

remove

public void remove(java.lang.String key)

Removes a redundant entry from the cache.

Specified by:

remove in interface StatementCache

Parameters:

key - value that identifies the cache entry

getObsoleteHandles

public java.util.Collection getObsoleteHandles(java.util.Collection handles)

Obtains a list of statement handles or procedures that can now be dropped.

Specified by:

getObsoleteHandles in interface StatementCache

Parameters:

handles - a collection of single use statements that will be returned for dropping if the cache is disabled

Returns:

the collection of redundant statments for dropping

scavengeCache

private void scavengeCache()

Removes unused entries trying to bring down the cache to the requested size. The removed entries are placed in the free list.

Note: entries that are in use will not be removed so it is possible for the cache to still be larger than cacheSize after the call finishes.