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}