    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.pool2;
    018
    019/**
    020 * An interface defining life-cycle methods for
    021 * instances to be served by a {@link KeyedObjectPool}.
    022 * <p>
    023 * By contract, when an {@link KeyedObjectPool}
    024 * delegates to a {@link KeyedPooledObjectFactory},
    025 * </p>
    026 * <ol>
    027 *  <li>
    028 *   {@link #makeObject} is called whenever a new instance is needed.
    029 *  </li>
    030 *  <li>
    031 *   {@link #activateObject} is invoked on every instance that has been
    032 *   {@link #passivateObject passivated} before it is
    033 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
    034 *  </li>
    035 *  <li>
    036 *   {@link #validateObject} may be invoked on {@link #activateObject activated}
    037 *   instances to make sure they can be
    038 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
    039 *   <code>validateObject</code> may also be used to test an
    040 *   instance being {@link KeyedObjectPool#returnObject returned} to the pool
    041 *   before it is {@link #passivateObject passivated}. It will only be invoked
    042 *   on an activated instance.
    043 *  </li>
    044 *  <li>
    045 *   {@link #passivateObject passivateObject}
    046 *   is invoked on every instance when it is returned to the pool.
    047 *  </li>
    048 *  <li>
    049 *   {@link #destroyObject destroyObject}
    050 *   is invoked on every instance when it is being "dropped" from the
    051 *   pool (whether due to the response from <code>validateObject</code>,
    052 *   or for reasons specific to the pool implementation.) There is no
    053 *   guarantee that the instance being destroyed will
    054 *   be considered active, passive or in a generally consistent state.
    055 *  </li>
    056 * </ol>
    057 * {@link KeyedPooledObjectFactory} must be thread-safe. The only promise
    058 * an {@link KeyedObjectPool} makes is that the same instance of an object will
    059 * not be passed to more than one method of a
    060 * <code>KeyedPoolableObjectFactory</code> at a time.
    061 * <p>
    062 * While clients of a {@link KeyedObjectPool} borrow and return instances of
    063 * the underlying value type V, the factory methods act on instances of
    064 * {@link PooledObject PooledObject&lt;V&gt;}.  These are the object wrappers that
    065 * pools use to track and maintain state informations about the objects that
    066 * they manage.
    067 * </p>
    068 *
    069 * @see KeyedObjectPool
    070 * @see BaseKeyedPooledObjectFactory
    071 *
    072 * @param <K> The type of keys managed by this factory.
    073 * @param <V> Type of element managed by this factory.
    074 *
    075 * @since 2.0
    076 */
    077public interface KeyedPooledObjectFactory<K, V> {
    078
    079    /**
    080     * Create an instance that can be served by the pool and
    081     * wrap it in a {@link PooledObject} to be managed by the pool.
    082     *
    083     * @param key the key used when constructing the object
    084     *
    085     * @return a {@code PooledObject} wrapping an instance that can
    086     * be served by the pool.
    087     *
    088     * @throws Exception if there is a problem creating a new instance,
    089     *    this will be propagated to the code requesting an object.
    090     */
    091    PooledObject<V> makeObject(K key) throws Exception;
    092
    093    /**
    094     * Destroy an instance no longer needed by the pool.
    095     * <p>
    096     * It is important for implementations of this method to be aware that there
    097     * is no guarantee about what state <code>obj</code> will be in and the
    098     * implementation should be prepared to handle unexpected errors.
    099     * </p>
    100     * <p>
    101     * Also, an implementation must take in to consideration that instances lost
    102     * to the garbage collector may never be destroyed.
    103     * </p>
    104     *
    105     * @param key the key used when selecting the instance
    106     * @param p a {@code PooledObject} wrapping the instance to be destroyed
    107     *
    108     * @throws Exception should be avoided as it may be swallowed by
    109     *    the pool implementation.
    110     *
    111     * @see #validateObject
    112     * @see KeyedObjectPool#invalidateObject
    113     */
    114    void destroyObject(K key, PooledObject<V> p) throws Exception;
    115
    116    /**
    117     * Ensures that the instance is safe to be returned by the pool.
    118     *
    119     * @param key the key used when selecting the object
    120     * @param p a {@code PooledObject} wrapping the instance to be validated
    121     *
    122     * @return <code>false</code> if <code>obj</code> is not valid and should
    123     *         be dropped from the pool, <code>true</code> otherwise.
    124     */
    125    boolean validateObject(K key, PooledObject<V> p);
    126
    127    /**
    128     * Reinitialize an instance to be returned by the pool.
    129     *
    130     * @param key the key used when selecting the object
    131     * @param p a {@code PooledObject} wrapping the instance to be activated
    132     *
    133     * @throws Exception if there is a problem activating <code>obj</code>,
    134     *    this exception may be swallowed by the pool.
    135     *
    136     * @see #destroyObject
    137     */
    138    void activateObject(K key, PooledObject<V> p) throws Exception;
    139
    140    /**
    141     * Uninitialize an instance to be returned to the idle object pool.
    142     *
    143     * @param key the key used when selecting the object
    144     * @param p a {@code PooledObject} wrapping the instance to be passivated
    145     *
    146     * @throws Exception if there is a problem passivating <code>obj</code>,
    147     *    this exception may be swallowed by the pool.
    148     *
    149     * @see #destroyObject
    150     */
    151    void passivateObject(K key, PooledObject<V> p) throws Exception;
    152}
    153