1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package org.apache.commons.pool; 19 20 /** 21 * An interface defining life-cycle methods for 22 * instances to be served by an {@link ObjectPool}. 23 * <p> 24 * By contract, when an {@link ObjectPool} 25 * delegates to a {@link PoolableObjectFactory}, 26 * <ol> 27 * <li> 28 * {@link #makeObject makeObject} 29 * is called whenever a new instance is needed. 30 * </li> 31 * <li> 32 * {@link #activateObject activateObject} 33 * is invoked on every instance that has been 34 * {@link #passivateObject passivated} before it is 35 * {@link ObjectPool#borrowObject borrowed} from the pool. 36 * </li> 37 * <li> 38 * {@link #validateObject validateObject} 39 * is invoked on {@link #activateObject activated} instances to make sure 40 * they can be {@link ObjectPool#borrowObject borrowed} from the pool. 41 * <code>validateObject</code> <strong>may</strong> also be used to test an 42 * instance being {@link ObjectPool#returnObject returned} to the pool 43 * before it is {@link #passivateObject passivated}. It will only be invoked 44 * on an activated instance. 45 * </li> 46 * <li> 47 * {@link #passivateObject passivateObject} 48 * is invoked on every instance when it is returned to the pool. 49 * </li> 50 * <li> 51 * {@link #destroyObject destroyObject} 52 * is invoked on every instance when it is being "dropped" from the 53 * pool (whether due to the response from <code>validateObject</code>, 54 * or for reasons specific to the pool implementation.) There is no 55 * guarantee that the instance being destroyed will 56 * be considered active, passive or in a generally consistent state. 57 * </li> 58 * </ol> 59 * </p> 60 * <p> 61 * {@link PoolableObjectFactory} must be thread-safe. The only promise 62 * an {@link ObjectPool} makes is that the same instance of an object will not 63 * be passed to more than one method of a <code>PoolableObjectFactory</code> 64 * at a time. 65 * </p> 66 * 67 * @see ObjectPool 68 * 69 * @author Rodney Waldhoff 70 * @author Sandy McArthur 71 * @version $Revision: 777748 $ $Date: 2009-05-22 17:00:44 -0700 (Fri, 22 May 2009) $ 72 * @since Pool 1.0 73 */ 74 public interface PoolableObjectFactory { 75 /** 76 * Creates an instance that can be served by the pool. 77 * Instances returned from this method should be in the 78 * same state as if they had been 79 * {@link #activateObject activated}. They will not be 80 * activated before being served by the pool. 81 * 82 * @return an instance that can be served by the pool. 83 * @throws Exception if there is a problem creating a new instance, 84 * this will be propagated to the code requesting an object. 85 */ 86 Object makeObject() throws Exception; 87 88 /** 89 * Destroys an instance no longer needed by the pool. 90 * <p> 91 * It is important for implementations of this method to be aware 92 * that there is no guarantee about what state <code>obj</code> 93 * will be in and the implementation should be prepared to handle 94 * unexpected errors. 95 * </p> 96 * <p> 97 * Also, an implementation must take in to consideration that 98 * instances lost to the garbage collector may never be destroyed. 99 * </p> 100 * 101 * @param obj the instance to be destroyed 102 * @throws Exception should be avoided as it may be swallowed by 103 * the pool implementation. 104 * @see #validateObject 105 * @see ObjectPool#invalidateObject 106 */ 107 void destroyObject(Object obj) throws Exception; 108 109 /** 110 * Ensures that the instance is safe to be returned by the pool. 111 * Returns <code>false</code> if <code>obj</code> should be destroyed. 112 * 113 * @param obj the instance to be validated 114 * @return <code>false</code> if <code>obj</code> is not valid and should 115 * be dropped from the pool, <code>true</code> otherwise. 116 */ 117 boolean validateObject(Object obj); 118 119 /** 120 * Reinitialize an instance to be returned by the pool. 121 * 122 * @param obj the instance to be activated 123 * @throws Exception if there is a problem activating <code>obj</code>, 124 * this exception may be swallowed by the pool. 125 * @see #destroyObject 126 */ 127 void activateObject(Object obj) throws Exception; 128 129 /** 130 * Uninitialize an instance to be returned to the idle object pool. 131 * 132 * @param obj the instance to be passivated 133 * @throws Exception if there is a problem passivating <code>obj</code>, 134 * this exception may be swallowed by the pool. 135 * @see #destroyObject 136 */ 137 void passivateObject(Object obj) throws Exception; 138 }