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 instances to be served by an
021 * {@link ObjectPool}.
022 * <p>
023 * By contract, when an {@link ObjectPool} delegates to a
024 * {@link PooledObjectFactory},
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 ObjectPool#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 {@link ObjectPool#borrowObject borrowed}
038 *   from the pool. {@link #validateObject} may also be used to
039 *   test an instance being {@link ObjectPool#returnObject returned} to the pool
040 *   before it is {@link #passivateObject passivated}. It will only be invoked
041 *   on an activated instance.
042 *  </li>
043 *  <li>
044 *   {@link #passivateObject} is invoked on every instance when it is returned
045 *   to the pool.
046 *  </li>
047 *  <li>
048 *   {@link #destroyObject} is invoked on every instance when it is being
049 *   "dropped" from the pool (whether due to the response from
050 *   {@link #validateObject}, or for reasons specific to the pool
051 *   implementation.) There is no guarantee that the instance being destroyed
052 *   will be considered active, passive or in a generally consistent state.
053 *  </li>
054 * </ol>
055 * {@link PooledObjectFactory} must be thread-safe. The only promise
056 * an {@link ObjectPool} makes is that the same instance of an object will not
057 * be passed to more than one method of a {@code PoolableObjectFactory}
058 * at a time.
059 * <p>
060 * While clients of a {@link KeyedObjectPool} borrow and return instances of
061 * the underlying value type {@code V}, the factory methods act on instances of
062 * {@link PooledObject PooledObject&lt;V&gt;}.  These are the object wrappers that
063 * pools use to track and maintain state information about the objects that
064 * they manage.
065 * </p>
066 *
067 * @param <T> Type of element managed in this factory.
068 *
069 * @see ObjectPool
070 *
071 * @since 2.0
072 */
073public interface PooledObjectFactory<T> {
074
075  /**
076   * Reinitializes an instance to be returned by the pool.
077   *
078   * @param p a {@code PooledObject} wrapping the instance to be activated
079   *
080   * @throws Exception if there is a problem activating {@code obj},
081   *    this exception may be swallowed by the pool.
082   *
083   * @see #destroyObject
084   */
085  void activateObject(PooledObject<T> p) throws Exception;
086
087  /**
088   * Destroys an instance no longer needed by the pool, using the default (NORMAL)
089   * DestroyMode.
090   * <p>
091   * It is important for implementations of this method to be aware that there
092   * is no guarantee about what state {@code obj} will be in and the
093   * implementation should be prepared to handle unexpected errors.
094   * </p>
095   * <p>
096   * Also, an implementation must take in to consideration that instances lost
097   * to the garbage collector may never be destroyed.
098   * </p>
099   *
100   * @param p a {@code PooledObject} wrapping the instance to be destroyed
101   *
102   * @throws Exception should be avoided as it may be swallowed by
103   *    the pool implementation.
104   *
105   * @see #validateObject
106   * @see ObjectPool#invalidateObject
107   */
108  void destroyObject(PooledObject<T> p) throws Exception;
109
110  /**
111   * Destroys an instance no longer needed by the pool, using the provided
112   * DestroyMode.
113   *
114   * @param p a {@code PooledObject} wrapping the instance to be destroyed
115   * @param destroyMode DestroyMode providing context to the factory
116   *
117   * @throws Exception should be avoided as it may be swallowed by
118   *    the pool implementation.
119   *
120   * @see #validateObject
121   * @see ObjectPool#invalidateObject
122   * @see #destroyObject(PooledObject)
123   * @see DestroyMode
124   * @since 2.9.0
125   */
126  default void destroyObject(final PooledObject<T> p, final DestroyMode destroyMode) throws Exception {
127      destroyObject(p);
128  }
129
130  /**
131   * Creates an instance that can be served by the pool and wrap it in a
132   * {@link PooledObject} to be managed by the pool.
133   *
134   * @return a {@code PooledObject} wrapping an instance that can be served by the pool, not null.
135   *
136   * @throws Exception if there is a problem creating a new instance,
137   *    this will be propagated to the code requesting an object.
138   */
139  PooledObject<T> makeObject() throws Exception;
140
141  /**
142   * Uninitializes an instance to be returned to the idle object pool.
143   *
144   * @param p a {@code PooledObject} wrapping the instance to be passivated
145   *
146   * @throws Exception if there is a problem passivating {@code obj},
147   *    this exception may be swallowed by the pool.
148   *
149   * @see #destroyObject
150   */
151  void passivateObject(PooledObject<T> p) throws Exception;
152
153  /**
154   * Ensures that the instance is safe to be returned by the pool.
155   *
156   * @param p a {@code PooledObject} wrapping the instance to be validated
157   *
158   * @return {@code false} if {@code obj} is not valid and should
159   *         be dropped from the pool, {@code true} otherwise.
160   */
161  boolean validateObject(PooledObject<T> p);
162}