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 an {@link ObjectPool}.
023 * <p>
024 * By contract, when an {@link ObjectPool}
025 * delegates to a {@link PoolableObjectFactory},
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 ObjectPool#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 ObjectPool#borrowObject borrowed} from the pool.
041 * <code>validateObject</code> <strong>may</strong> also be used to test an
042 * instance being {@link ObjectPool#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 PoolableObjectFactory} must be thread-safe. The only promise
062 * an {@link ObjectPool} makes is that the same instance of an object will not
063 * be passed to more than one method of a <code>PoolableObjectFactory</code>
064 * at a time.
065 * </p>
066 *
067 * @param <T> the type of objects held in this pool
068 *
069 * @see ObjectPool
070 *
071 * @author Rodney Waldhoff
072 * @author Sandy McArthur
073 * @version $Revision: 1222388 $ $Date: 2011-12-22 13:28:27 -0500 (Thu, 22 Dec 2011) $
074 * @since Pool 1.0
075 */
076 public interface PoolableObjectFactory<T> {
077 /**
078 * Creates an instance that can be served by the pool.
079 * Instances returned from this method should be in the
080 * same state as if they had been
081 * {@link #activateObject activated}. They will not be
082 * activated before being served by the pool.
083 *
084 * @return an instance that can be served by the pool.
085 * @throws Exception if there is a problem creating a new instance,
086 * this will be propagated to the code requesting an object.
087 */
088 T makeObject() throws Exception;
089
090 /**
091 * Destroys an instance no longer needed by the pool.
092 * <p>
093 * It is important for implementations of this method to be aware
094 * that there is no guarantee about what state <code>obj</code>
095 * will be in and the implementation should be prepared to handle
096 * unexpected errors.
097 * </p>
098 * <p>
099 * Also, an implementation must take in to consideration that
100 * instances lost to the garbage collector may never be destroyed.
101 * </p>
102 *
103 * @param obj the instance to be destroyed
104 * @throws Exception should be avoided as it may be swallowed by
105 * the pool implementation.
106 * @see #validateObject
107 * @see ObjectPool#invalidateObject
108 */
109 void destroyObject(T obj) throws Exception;
110
111 /**
112 * Ensures that the instance is safe to be returned by the pool.
113 * Returns <code>false</code> if <code>obj</code> should be destroyed.
114 *
115 * @param obj the instance to be validated
116 * @return <code>false</code> if <code>obj</code> is not valid and should
117 * be dropped from the pool, <code>true</code> otherwise.
118 */
119 boolean validateObject(T obj);
120
121 /**
122 * Reinitialize an instance to be returned by the pool.
123 *
124 * @param obj the instance to be activated
125 * @throws Exception if there is a problem activating <code>obj</code>,
126 * this exception may be swallowed by the pool.
127 * @see #destroyObject
128 */
129 void activateObject(T obj) throws Exception;
130
131 /**
132 * Uninitialize an instance to be returned to the idle object pool.
133 *
134 * @param obj the instance to be passivated
135 * @throws Exception if there is a problem passivating <code>obj</code>,
136 * this exception may be swallowed by the pool.
137 * @see #destroyObject
138 */
139 void passivateObject(T obj) throws Exception;
140 }