KeyedPooledObjectFactory.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.tomcat.dbcp.pool2;
/**
* 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} 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},
* 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 KeyedPooledObjectFactory} 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<V>}. These are the object wrappers that
* pools use to track and maintain state informations about the objects that
* they manage.
* </p>
*
* @see KeyedObjectPool
*
* @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> {
/**
* Reinitializes 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},
* this exception may be swallowed by the pool.
*
* @see #destroyObject
*/
void activateObject(K key, PooledObject<V> p) throws Exception;
/**
* Destroys 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} 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;
/**
* Destroys an instance no longer needed by the pool, using the provided {@link DestroyMode}.
*
* @param key the key used when selecting the instance
* @param p a {@code PooledObject} wrapping the instance to be destroyed
* @param destroyMode DestroyMode providing context to the factory
*
* @throws Exception should be avoided as it may be swallowed by
* the pool implementation.
*
* @see #validateObject
* @see KeyedObjectPool#invalidateObject
* @see #destroyObject(Object, PooledObject)
* @see DestroyMode
* @since 2.9.0
*/
default void destroyObject(final K key, final PooledObject<V> p, final DestroyMode destroyMode) throws Exception {
destroyObject(key, p);
}
/**
* Creates 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;
/**
* Uninitializes 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},
* this exception may be swallowed by the pool.
*
* @see #destroyObject
*/
void passivateObject(K key, PooledObject<V> p) throws Exception;
/**
* 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} if {@code obj} is not valid and should
* be dropped from the pool, {@code true} otherwise.
*/
boolean validateObject(K key, PooledObject<V> p);
}