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 * @see ObjectPool
069 * @since 2.0
070 */
071public interface PooledObjectFactory<T> {
072
073  /**
074   * Reinitializes an instance to be returned by the pool.
075   *
076   * @param p a {@code PooledObject} wrapping the instance to be activated
077   * @throws Exception if there is a problem activating {@code obj},
078   *    this exception may be swallowed by the pool.
079   *
080   * @see #destroyObject
081   */
082  void activateObject(PooledObject<T> p) throws Exception;
083
084  /**
085   * Destroys an instance no longer needed by the pool, using the default (NORMAL)
086   * DestroyMode.
087   * <p>
088   * It is important for implementations of this method to be aware that there
089   * is no guarantee about what state {@code obj} will be in and the
090   * implementation should be prepared to handle unexpected errors.
091   * </p>
092   * <p>
093   * Also, an implementation must take in to consideration that instances lost
094   * to the garbage collector may never be destroyed.
095   * </p>
096   *
097   * @param p a {@code PooledObject} wrapping the instance to be destroyed
098   * @throws Exception should be avoided as it may be swallowed by
099   *    the pool implementation.
100   *
101   * @see #validateObject
102   * @see ObjectPool#invalidateObject
103   */
104  void destroyObject(PooledObject<T> p) throws Exception;
105
106  /**
107   * Destroys an instance no longer needed by the pool, using the provided
108   * DestroyMode.
109   *
110   * @param p a {@code PooledObject} wrapping the instance to be destroyed
111   * @param destroyMode DestroyMode providing context to the factory
112   * @throws Exception should be avoided as it may be swallowed by
113   *    the pool implementation.
114   *
115   * @see #validateObject
116   * @see ObjectPool#invalidateObject
117   * @see #destroyObject(PooledObject)
118   * @see DestroyMode
119   * @since 2.9.0
120   */
121  default void destroyObject(final PooledObject<T> p, final DestroyMode destroyMode) throws Exception {
122      destroyObject(p);
123  }
124
125  /**
126   * Creates an instance that can be served by the pool and wrap it in a
127   * {@link PooledObject} to be managed by the pool.
128   *
129   * @return a {@code PooledObject} wrapping an instance that can be served by the pool, not null.
130   * @throws Exception if there is a problem creating a new instance,
131   *    this will be propagated to the code requesting an object.
132   */
133  PooledObject<T> makeObject() throws Exception;
134
135  /**
136   * Uninitializes an instance to be returned to the idle object pool.
137   *
138   * @param p a {@code PooledObject} wrapping the instance to be passivated
139   * @throws Exception if there is a problem passivating {@code obj},
140   *    this exception may be swallowed by the pool.
141   *
142   * @see #destroyObject
143   */
144  void passivateObject(PooledObject<T> p) throws Exception;
145
146  /**
147   * Ensures that the instance is safe to be returned by the pool.
148   *
149   * @param p a {@code PooledObject} wrapping the instance to be validated
150   * @return {@code false} if {@code obj} is not valid and should
151   *         be dropped from the pool, {@code true} otherwise.
152   */
153  boolean validateObject(PooledObject<T> p);
154}