    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 * <ol>
    026 *  <li>
    027 *   {@link #makeObject} is called whenever a new instance is needed.
    028 *  </li>
    029 *  <li>
    030 *   {@link #activateObject} is invoked on every instance that has been
    031 *   {@link #passivateObject passivated} before it is
    032 *   {@link ObjectPool#borrowObject borrowed} from the pool.
    033 *  </li>
    034 *  <li>
    035 *   {@link #validateObject} may be invoked on {@link #activateObject activated}
    036 *   instances to make sure they can be {@link ObjectPool#borrowObject borrowed}
    037 *   from the pool. {@link #validateObject} may also be used to
    038 *   test an instance being {@link ObjectPool#returnObject returned} to the pool
    039 *   before it is {@link #passivateObject passivated}. It will only be invoked
    040 *   on an activated instance.
    041 *  </li>
    042 *  <li>
    043 *   {@link #passivateObject} is invoked on every instance when it is returned
    044 *   to the pool.
    045 *  </li>
    046 *  <li>
    047 *   {@link #destroyObject} is invoked on every instance when it is being
    048 *   "dropped" from the pool (whether due to the response from
    049 *   {@link #validateObject}, or for reasons specific to the pool
    050 *   implementation.) There is no guarantee that the instance being destroyed
    051 *   will be considered active, passive or in a generally consistent state.
    052 *  </li>
    053 * </ol>
    054 * {@link PooledObjectFactory} must be thread-safe. The only promise
    055 * an {@link ObjectPool} makes is that the same instance of an object will not
    056 * be passed to more than one method of a <code>PoolableObjectFactory</code>
    057 * at a time.
    058 * <p>
    059 * While clients of a {@link KeyedObjectPool} borrow and return instances of
    060 * the underlying value type {@code V}, the factory methods act on instances of
    061 * {@link PooledObject PooledObject<V>}.  These are the object wrappers that
    062 * pools use to track and maintain state information about the objects that
    063 * they manage.
    064 *
    065 * @param <T> Type of element managed in this factory.
    066 *
    067 * @see ObjectPool
    068 *
    069 * @version $Revision: 1333925 $
    070 *
    071 * @since 2.0
    072 */
    073public interface PooledObjectFactory<T> {
    074  /**
    075   * Create an instance that can be served by the pool and wrap it in a
    076   * {@link PooledObject} to be managed by the pool.
    077   *
    078   * @return a {@code PooledObject} wrapping an instance that can be served by the pool
    079   *
    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  PooledObject<T> makeObject() throws Exception;
    084
    085  /**
    086   * Destroys an instance no longer needed by the pool.
    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</code> will be in and the
    090   * implementation should be prepared to handle unexpected errors.
    091   * <p>
    092   * Also, an implementation must take in to consideration that instances lost
    093   * to the garbage collector may never be destroyed.
    094   * </p>
    095   *
    096   * @param p a {@code PooledObject} wrapping the instance to be destroyed
    097   *
    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   * Ensures that the instance is safe to be returned by the pool.
    108   *
    109   * @param p a {@code PooledObject} wrapping the instance to be validated
    110   *
    111   * @return <code>false</code> if <code>obj</code> is not valid and should
    112   *         be dropped from the pool, <code>true</code> otherwise.
    113   */
    114  boolean validateObject(PooledObject<T> p);
    115
    116  /**
    117   * Reinitialize an instance to be returned by the pool.
    118   *
    119   * @param p a {@code PooledObject} wrapping the instance to be activated
    120   *
    121   * @throws Exception if there is a problem activating <code>obj</code>,
    122   *    this exception may be swallowed by the pool.
    123   *
    124   * @see #destroyObject
    125   */
    126  void activateObject(PooledObject<T> p) throws Exception;
    127
    128  /**
    129   * Uninitialize an instance to be returned to the idle object pool.
    130   *
    131   * @param p a {@code PooledObject} wrapping the instance to be passivated
    132   *
    133   * @throws Exception if there is a problem passivating <code>obj</code>,
    134   *    this exception may be swallowed by the pool.
    135   *
    136   * @see #destroyObject
    137   */
    138  void passivateObject(PooledObject<T> p) throws Exception;
    139}