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package org.apache.commons.pool2;

An interface defining life-cycle methods for instances to be served by a KeyedObjectPool. 
 By contract, when an KeyedObjectPool delegates to a KeyedPooledObjectFactory, 

 
 makeObject is called whenever a new instance is needed. 
 
 activateObject is invoked on every instance that has been passivated before it is borrowed from the pool. 
 
 validateObject may be 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. 
 
 passivateObject is invoked on every instance when it is returned to the pool. 
 
 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.
 
 KeyedPooledObjectFactory must be thread-safe. The only promise an KeyedObjectPool makes is that the same instance of an object will not be passed to more than one method of a KeyedPoolableObjectFactory at a time.
 While clients of a KeyedObjectPool borrow and return instances of the underlying value type V, the factory methods act on instances of PooledObject<V>. These are the object wrappers that pools use to track and maintain state informations about the objects that they manage. 
Type parameters:
<K> – The type of keys managed by this factory.
<V> – Type of element managed by this factory.
See Also:
KeyedObjectPool
BaseKeyedPooledObjectFactory
Since:
2.0/**
 * An interface defining life-cycle methods for
 * instances to be served by a {@link KeyedObjectPool}.
 * <p>
 * By contract, when an {@link KeyedObjectPool}
 * delegates to a {@link KeyedPooledObjectFactory},
 * </p>
 * <ol>
 *  <li>
 *   {@link #makeObject} is called whenever a new instance is needed.
 *  </li>
 *  <li>
 *   {@link #activateObject} is invoked on every instance that has been
 *   {@link #passivateObject passivated} before it is
 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
 *  </li>
 *  <li>
 *   {@link #validateObject} may be invoked on {@link #activateObject activated}
 *   instances to make sure they can be
 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
 *   <code>validateObject</code> may also be used to test an
 *   instance being {@link KeyedObjectPool#returnObject returned} to the pool
 *   before it is {@link #passivateObject passivated}. It will only be invoked
 *   on an activated instance.
 *  </li>
 *  <li>
 *   {@link #passivateObject passivateObject}
 *   is invoked on every instance when it is returned to the pool.
 *  </li>
 *  <li>
 *   {@link #destroyObject destroyObject}
 *   is invoked on every instance when it is being "dropped" from the
 *   pool (whether due to the response from <code>validateObject</code>,
 *   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.
 *  </li>
 * </ol>
 * {@link KeyedPooledObjectFactory} must be thread-safe. The only promise
 * an {@link KeyedObjectPool} makes is that the same instance of an object will
 * not be passed to more than one method of a
 * <code>KeyedPoolableObjectFactory</code> at a time.
 * <p>
 * While clients of a {@link KeyedObjectPool} borrow and return instances of
 * the underlying value type V, the factory methods act on instances of
 * {@link PooledObject PooledObject&lt;V&gt;}.  These are the object wrappers that
 * pools use to track and maintain state informations about the objects that
 * they manage.
 * </p>
 *
 * @see KeyedObjectPool
 * @see BaseKeyedPooledObjectFactory
 *
 * @param <K> The type of keys managed by this factory.
 * @param <V> Type of element managed by this factory.
 *
 * @since 2.0
 */
public interface KeyedPooledObjectFactory<K, V> {

    
Create an instance that can be served by the pool and wrap it in a PooledObject to be managed by the pool. 
Params:
key – the key used when constructing the object
Throws:
Exception – if there is a problem creating a new instance,
   this will be propagated to the code requesting an object.
Returns:
a PooledObject wrapping an instance that can be served by the pool./**
     * Create an instance that can be served by the pool and
     * wrap it in a {@link PooledObject} to be managed by the pool.
     *
     * @param key the key used when constructing the object
     *
     * @return a {@code PooledObject} wrapping 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.
     */
    PooledObject<V> makeObject(K key) throws Exception;

    
Destroy 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.

Params:
key – the key used when selecting the instance
p – a PooledObject wrapping the instance to be destroyed
Throws:
Exception – should be avoided as it may be swallowed by
   the pool implementation.
See Also:
validateObject
KeyedObjectPool.invalidateObject/**
     * Destroy an instance no longer needed by the pool.
     * <p>
     * It is important for implementations of this method to be aware that there
     * is no guarantee about what state <code>obj</code> will be in and the
     * implementation should be prepared to handle unexpected errors.
     * </p>
     * <p>
     * Also, an implementation must take in to consideration that instances lost
     * to the garbage collector may never be destroyed.
     * </p>
     *
     * @param key the key used when selecting the instance
     * @param p a {@code PooledObject} wrapping the instance to be destroyed
     *
     * @throws Exception should be avoided as it may be swallowed by
     *    the pool implementation.
     *
     * @see #validateObject
     * @see KeyedObjectPool#invalidateObject
     */
    void destroyObject(K key, PooledObject<V> p) throws Exception;

    
Ensures that the instance is safe to be returned by the pool.
Params:
key – the key used when selecting the object
p – a PooledObject wrapping the instance to be validated
Returns:
false if obj is not valid and should
        be dropped from the pool, true otherwise./**
     * Ensures that the instance is safe to be returned by the pool.
     *
     * @param key the key used when selecting the object
     * @param p a {@code PooledObject} wrapping the instance to be validated
     *
     * @return <code>false</code> if <code>obj</code> is not valid and should
     *         be dropped from the pool, <code>true</code> otherwise.
     */
    boolean validateObject(K key, PooledObject<V> p);

    
Reinitialize an instance to be returned by the pool.
Params:
key – the key used when selecting the object
p – a PooledObject wrapping 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/**
     * Reinitialize an instance to be returned by the pool.
     *
     * @param key the key used when selecting the object
     * @param p a {@code PooledObject} wrapping the instance to be activated
     *
     * @throws Exception if there is a problem activating <code>obj</code>,
     *    this exception may be swallowed by the pool.
     *
     * @see #destroyObject
     */
    void activateObject(K key, PooledObject<V> p) throws Exception;

    
Uninitialize an instance to be returned to the idle object pool.
Params:
key – the key used when selecting the object
p – a PooledObject wrapping 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/**
     * Uninitialize an instance to be returned to the idle object pool.
     *
     * @param key the key used when selecting the object
     * @param p a {@code PooledObject} wrapping the instance to be passivated
     *
     * @throws Exception if there is a problem passivating <code>obj</code>,
     *    this exception may be swallowed by the pool.
     *
     * @see #destroyObject
     */
    void passivateObject(K key, PooledObject<V> p) throws Exception;
}