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 */ 017 018 package org.apache.commons.pool; 019 020 /** 021 * An interface defining life-cycle methods for 022 * instances to be served by an {@link ObjectPool}. 023 * <p> 024 * By contract, when an {@link ObjectPool} 025 * delegates to a {@link PoolableObjectFactory}, 026 * <ol> 027 * <li> 028 * {@link #makeObject makeObject} 029 * is called whenever a new instance is needed. 030 * </li> 031 * <li> 032 * {@link #activateObject activateObject} 033 * is invoked on every instance that has been 034 * {@link #passivateObject passivated} before it is 035 * {@link ObjectPool#borrowObject borrowed} from the pool. 036 * </li> 037 * <li> 038 * {@link #validateObject validateObject} 039 * is invoked on {@link #activateObject activated} instances to make sure 040 * they can be {@link ObjectPool#borrowObject borrowed} from the pool. 041 * <code>validateObject</code> <strong>may</strong> also be used to test an 042 * instance being {@link ObjectPool#returnObject returned} to the pool 043 * before it is {@link #passivateObject passivated}. It will only be invoked 044 * on an activated instance. 045 * </li> 046 * <li> 047 * {@link #passivateObject passivateObject} 048 * is invoked on every instance when it is returned to the pool. 049 * </li> 050 * <li> 051 * {@link #destroyObject destroyObject} 052 * is invoked on every instance when it is being "dropped" from the 053 * pool (whether due to the response from <code>validateObject</code>, 054 * or for reasons specific to the pool implementation.) There is no 055 * guarantee that the instance being destroyed will 056 * be considered active, passive or in a generally consistent state. 057 * </li> 058 * </ol> 059 * </p> 060 * <p> 061 * {@link PoolableObjectFactory} must be thread-safe. The only promise 062 * an {@link ObjectPool} makes is that the same instance of an object will not 063 * be passed to more than one method of a <code>PoolableObjectFactory</code> 064 * at a time. 065 * </p> 066 * 067 * @param <T> the type of objects held in this pool 068 * 069 * @see ObjectPool 070 * 071 * @author Rodney Waldhoff 072 * @author Sandy McArthur 073 * @version $Revision: 1222388 $ $Date: 2011-12-22 13:28:27 -0500 (Thu, 22 Dec 2011) $ 074 * @since Pool 1.0 075 */ 076 public interface PoolableObjectFactory<T> { 077 /** 078 * Creates an instance that can be served by the pool. 079 * Instances returned from this method should be in the 080 * same state as if they had been 081 * {@link #activateObject activated}. They will not be 082 * activated before being served by the pool. 083 * 084 * @return an instance that can be served by the pool. 085 * @throws Exception if there is a problem creating a new instance, 086 * this will be propagated to the code requesting an object. 087 */ 088 T makeObject() throws Exception; 089 090 /** 091 * Destroys an instance no longer needed by the pool. 092 * <p> 093 * It is important for implementations of this method to be aware 094 * that there is no guarantee about what state <code>obj</code> 095 * will be in and the implementation should be prepared to handle 096 * unexpected errors. 097 * </p> 098 * <p> 099 * Also, an implementation must take in to consideration that 100 * instances lost to the garbage collector may never be destroyed. 101 * </p> 102 * 103 * @param obj the instance to be destroyed 104 * @throws Exception should be avoided as it may be swallowed by 105 * the pool implementation. 106 * @see #validateObject 107 * @see ObjectPool#invalidateObject 108 */ 109 void destroyObject(T obj) throws Exception; 110 111 /** 112 * Ensures that the instance is safe to be returned by the pool. 113 * Returns <code>false</code> if <code>obj</code> should be destroyed. 114 * 115 * @param obj the instance to be validated 116 * @return <code>false</code> if <code>obj</code> is not valid and should 117 * be dropped from the pool, <code>true</code> otherwise. 118 */ 119 boolean validateObject(T obj); 120 121 /** 122 * Reinitialize an instance to be returned by the pool. 123 * 124 * @param obj the instance to be activated 125 * @throws Exception if there is a problem activating <code>obj</code>, 126 * this exception may be swallowed by the pool. 127 * @see #destroyObject 128 */ 129 void activateObject(T obj) throws Exception; 130 131 /** 132 * Uninitialize an instance to be returned to the idle object pool. 133 * 134 * @param obj the instance to be passivated 135 * @throws Exception if there is a problem passivating <code>obj</code>, 136 * this exception may be swallowed by the pool. 137 * @see #destroyObject 138 */ 139 void passivateObject(T obj) throws Exception; 140 }