    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} 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},
    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 KeyedPooledObjectFactory} 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     * Reinitializes an instance to be returned by the pool.
    081     *
    082     * @param key the key used when selecting the object
    083     * @param p a {@code PooledObject} wrapping the instance to be activated
    084     *
    085     * @throws Exception if there is a problem activating {@code obj},
    086     *    this exception may be swallowed by the pool.
    087     *
    088     * @see #destroyObject
    089     */
    090    void activateObject(K key, PooledObject<V> p) throws Exception;
    091
    092    /**
    093     * Destroys an instance no longer needed by the pool.
    094     * <p>
    095     * It is important for implementations of this method to be aware that there
    096     * is no guarantee about what state {@code obj} will be in and the
    097     * implementation should be prepared to handle unexpected errors.
    098     * </p>
    099     * <p>
    100     * Also, an implementation must take in to consideration that instances lost
    101     * to the garbage collector may never be destroyed.
    102     * </p>
    103     *
    104     * @param key the key used when selecting the instance
    105     * @param p a {@code PooledObject} wrapping the instance to be destroyed
    106     *
    107     * @throws Exception should be avoided as it may be swallowed by
    108     *    the pool implementation.
    109     *
    110     * @see #validateObject
    111     * @see KeyedObjectPool#invalidateObject
    112     */
    113    void destroyObject(K key, PooledObject<V> p) throws Exception;
    114
    115    /**
    116     * Destroys an instance no longer needed by the pool, using the provided {@link DestroyMode}.
    117     *
    118     * @param key the key used when selecting the instance
    119     * @param p a {@code PooledObject} wrapping the instance to be destroyed
    120     * @param destroyMode DestroyMode providing context to the factory
    121     *
    122     * @throws Exception should be avoided as it may be swallowed by
    123     *    the pool implementation.
    124     *
    125     * @see #validateObject
    126     * @see KeyedObjectPool#invalidateObject
    127     * @see #destroyObject(Object, PooledObject)
    128     * @see DestroyMode
    129     * @since 2.9.0
    130     */
    131    default void destroyObject(final K key, final PooledObject<V> p, final DestroyMode destroyMode) throws Exception {
    132        destroyObject(key, p);
    133    }
    134
    135    /**
    136     * Creates an instance that can be served by the pool and
    137     * wrap it in a {@link PooledObject} to be managed by the pool.
    138     *
    139     * @param key the key used when constructing the object
    140     *
    141     * @return a {@code PooledObject} wrapping an instance that can
    142     * be served by the pool.
    143     *
    144     * @throws Exception if there is a problem creating a new instance,
    145     *    this will be propagated to the code requesting an object.
    146     */
    147    PooledObject<V> makeObject(K key) throws Exception;
    148
    149    /**
    150     * Uninitializes an instance to be returned to the idle object pool.
    151     *
    152     * @param key the key used when selecting the object
    153     * @param p a {@code PooledObject} wrapping the instance to be passivated
    154     *
    155     * @throws Exception if there is a problem passivating {@code obj},
    156     *    this exception may be swallowed by the pool.
    157     *
    158     * @see #destroyObject
    159     */
    160    void passivateObject(K key, PooledObject<V> p) throws Exception;
    161
    162    /**
    163     * Ensures that the instance is safe to be returned by the pool.
    164     *
    165     * @param key the key used when selecting the object
    166     * @param p a {@code PooledObject} wrapping the instance to be validated
    167     *
    168     * @return {@code false} if {@code obj} is not valid and should
    169     *         be dropped from the pool, {@code true} otherwise.
    170     */
    171    boolean validateObject(K key, PooledObject<V> p);
    172}
    173