org.apache.commons.pool
Interface PoolableObjectFactory

All Known Implementing Classes:

BasePoolableObjectFactory

public interface PoolableObjectFactory

An interface defining life-cycle methods for instances to be served by an ObjectPool.

By contract, when an ObjectPool delegates to a PoolableObjectFactory,

1. makeObject is called whenever a new instance is needed.
2. activateObject is invoked on every instance that has been passivated before it is borrowed from the pool.
3. validateObject is invoked on activated instances to make sure they can be borrowed from the pool. validateObject may also be used to test an instance being returned to the pool before it is passivated. It will only be invoked on an activated instance.
4. passivateObject is invoked on every instance when it is returned to the pool.
5. destroyObject is invoked on every instance when it is being "dropped" from the pool (whether due to the response from validateObject, or for reasons specific to the pool implementation.) There is no guarantee that the instance being destroyed will be considered active, passive or in a generally consistent state.

PoolableObjectFactory must be thread-safe. The only promise an ObjectPool makes is that the same instance of an object will not be passed to more than one method of a PoolableObjectFactory at a time.

Since:

Pool 1.0

Version:

$Revision: 777748 $ $Date: 2009-05-22 20:00:44 -0400 (Fri, 22 May 2009) $

Author:

Rodney Waldhoff, Sandy McArthur

See Also:

ObjectPool

Method Summary

void	activateObject(Object obj) Reinitialize an instance to be returned by the pool.
void	destroyObject(Object obj) Destroys an instance no longer needed by the pool.
Object	makeObject() Creates an instance that can be served by the pool.
void	passivateObject(Object obj) Uninitialize an instance to be returned to the idle object pool.
boolean	validateObject(Object obj) Ensures that the instance is safe to be returned by the pool.

Method Detail

makeObject

Object makeObject()
                  throws Exception

Creates an instance that can be served by the pool. Instances returned from this method should be in the same state as if they had been activated. They will not be activated before being served by the pool.

Returns:

an instance that can be served by the pool.

Throws:

Exception - if there is a problem creating a new instance, this will be propagated to the code requesting an object.

destroyObject

void destroyObject(Object obj)
                   throws Exception

Destroys an instance no longer needed by the pool.

It is important for implementations of this method to be aware that there is no guarantee about what state obj will be in and the implementation should be prepared to handle unexpected errors.

Also, an implementation must take in to consideration that instances lost to the garbage collector may never be destroyed.

Parameters:

obj - the instance to be destroyed

Throws:

Exception - should be avoided as it may be swallowed by the pool implementation.

See Also:

validateObject(java.lang.Object), ObjectPool.invalidateObject(java.lang.Object)

validateObject

boolean validateObject(Object obj)

Ensures that the instance is safe to be returned by the pool. Returns false if obj should be destroyed.

Parameters:

obj - the instance to be validated

Returns:

false if obj is not valid and should be dropped from the pool, true otherwise.

activateObject

void activateObject(Object obj)
                    throws Exception

Reinitialize an instance to be returned by the pool.

Parameters:

obj - the instance to be activated

Throws:

Exception - if there is a problem activating obj, this exception may be swallowed by the pool.

See Also:

destroyObject(java.lang.Object)

passivateObject

void passivateObject(Object obj)
                     throws Exception

Uninitialize an instance to be returned to the idle object pool.

Parameters:

obj - the instance to be passivated

Throws:

Exception - if there is a problem passivating obj, this exception may be swallowed by the pool.

See Also:

destroyObject(java.lang.Object)