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