PooledObjectFactory

PooledObjectFactory provides a generic interface for managing the lifecycle of a pooled object:

public interface PooledObjectFactory<T> {
    activateObject(PooledObject<T>)
    destroyObject(PooledObject<T>)
    destroyObject(PooledObject<T>, DestroyMode)
    makeObject()
    passivateObject(PooledObject<T>)
    validateObject(PooledObject<T>)
}

Users of 1.x versions of Commons Pool will notice that while the PoolableObjectFactorys used by 1.x pools create and manage pooled objects directly, version 2 PooledObjectFactorys create and manage PooledObjects. These object wrappers maintain object pooling state, enabling PooledObjectFactory methods to have access to data such as instance creation time or time of last use. A DefaultPooledObject is provided, with natural implementations for pooling state methods. The simplest way to implement a PoolableObjectFactory is to have it extend BasePooledObjectFactory. This factory provides a makeObject() that returns wrap(create()) where create and wrap are abstract. You provide an implementation of create to create the underlying objects that you want to manage in the pool and wrap to wrap created instances in PooledObjects. To use DefaultPooledObject wrappers, use

@Override
 public PooledObject<Foo> wrap(Foo foo) {
    return new DefaultPooledObject<Foo>(foo);
 }
 

KeyedPooledObjectFactory defines a similar interface for KeyedObjectPools:

public interface KeyedPooledObjectFactory<K,V> {
    PooledObject<V> makeObject(K key);
    void activateObject(K key, PooledObject<V> obj);
    void passivateObject(K key, PooledObject<V> obj);
    boolean validateObject(K key, PooledObject<V> obj);
    void destroyObject(K key, PooledObject<V> obj);
}

BaseKeyedPooledObjectFactory provides an abstract base implementation of KeyedPooledObjectFactory.

GenericObjectPool

GenericObjectPool provides a wide variety of configuration options, including the ability to cap the number of idle or active instances, to evict instances as they sit idle in the pool, etc. As of version 2, GenericObjectPool also provides abandoned instance tracking and removal.

GenericKeyedObjectPool offers the same behavior for keyed pools.

SoftReferenceObjectPool

SoftReferenceObjectPool can grow as needed, but allows the garbage collector to evict idle instances from the pool as needed.