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