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 */
017
018 package org.apache.commons.pool;
019
020 /**
021 * An interface defining life-cycle methods for
022 * instances to be served by a {@link KeyedObjectPool}.
023 * <p>
024 * By contract, when an {@link KeyedObjectPool}
025 * delegates to a {@link KeyedPoolableObjectFactory},
026 * <ol>
027 * <li>
028 * {@link #makeObject makeObject}
029 * is called whenever a new instance is needed.
030 * </li>
031 * <li>
032 * {@link #activateObject activateObject}
033 * is invoked on every instance that has been
034 * {@link #passivateObject passivated} before it is
035 * {@link KeyedObjectPool#borrowObject borrowed} from the pool.
036 * </li>
037 * <li>
038 * {@link #validateObject validateObject}
039 * is invoked on {@link #activateObject activated} instances to make sure
040 * they can be {@link KeyedObjectPool#borrowObject borrowed} from the pool.
041 * <code>validateObject</code> <strong>may</strong> also be used to test an
042 * instance being {@link KeyedObjectPool#returnObject returned} to the pool
043 * before it is {@link #passivateObject passivated}. It will only be invoked
044 * on an activated instance.
045 * </li>
046 * <li>
047 * {@link #passivateObject passivateObject}
048 * is invoked on every instance when it is returned to the pool.
049 * </li>
050 * <li>
051 * {@link #destroyObject destroyObject}
052 * is invoked on every instance when it is being "dropped" from the
053 * pool (whether due to the response from <code>validateObject</code>,
054 * or for reasons specific to the pool implementation.) There is no
055 * guarantee that the instance being destroyed will
056 * be considered active, passive or in a generally consistent state.
057 * </li>
058 * </ol>
059 * </p>
060 * <p>
061 * {@link KeyedPoolableObjectFactory} must be thread-safe. The only promise
062 * an {@link KeyedObjectPool} makes is that the same instance of an object will not
063 * be passed to more than one method of a <code>KeyedPoolableObjectFactory</code>
064 * at a time.
065 * </p>
066 *
067 * @see KeyedObjectPool
068 *
069 * @author Rodney Waldhoff
070 * @author Sandy McArthur
071 * @version $Revision: 791676 $ $Date: 2009-07-06 19:29:56 -0700 (Mon, 06 Jul 2009) $
072 * @since Pool 1.0
073 */
074 public interface KeyedPoolableObjectFactory {
075 /**
076 * Create an instance that can be served by the pool.
077 *
078 * @param key the key used when constructing the object
079 * @return an instance that can be served by the pool.
080 * @throws Exception if there is a problem creating a new instance,
081 * this will be propagated to the code requesting an object.
082 */
083 Object makeObject(Object key) throws Exception;
084
085 /**
086 * Destroy an instance no longer needed by the pool.
087 * <p>
088 * It is important for implementations of this method to be aware
089 * that there is no guarantee about what state <code>obj</code>
090 * will be in and the implementation should be prepared to handle
091 * unexpected errors.
092 * </p>
093 * <p>
094 * Also, an implementation must take in to consideration that
095 * instances lost to the garbage collector may never be destroyed.
096 * </p>
097 *
098 * @param key the key used when selecting the instance
099 * @param obj the instance to be destroyed
100 * @throws Exception should be avoided as it may be swallowed by
101 * the pool implementation.
102 * @see #validateObject
103 * @see KeyedObjectPool#invalidateObject
104 */
105 void destroyObject(Object key, Object obj) throws Exception;
106
107 /**
108 * Ensures that the instance is safe to be returned by the pool.
109 * Returns <code>false</code> if <code>obj</code> should be destroyed.
110 *
111 * @param key the key used when selecting the object
112 * @param obj the instance to be validated
113 * @return <code>false</code> if <code>obj</code> is not valid and should
114 * be dropped from the pool, <code>true</code> otherwise.
115 */
116 boolean validateObject(Object key, Object obj);
117
118 /**
119 * Reinitialize an instance to be returned by the pool.
120 *
121 * @param key the key used when selecting the object
122 * @param obj the instance to be activated
123 * @throws Exception if there is a problem activating <code>obj</code>,
124 * this exception may be swallowed by the pool.
125 * @see #destroyObject
126 */
127 void activateObject(Object key, Object obj) throws Exception;
128
129 /**
130 * Uninitialize an instance to be returned to the idle object pool.
131 *
132 * @param key the key used when selecting the object
133 * @param obj the instance to be passivated
134 * @throws Exception if there is a problem passivating <code>obj</code>,
135 * this exception may be swallowed by the pool.
136 * @see #destroyObject
137 */
138 void passivateObject(Object key, Object obj) throws Exception;
139 }