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 import java.util.NoSuchElementException; 021 022 /** 023 * A pooling interface. 024 * <p> 025 * <code>ObjectPool</code> defines a trivially simple pooling interface. The only 026 * required methods are {@link #borrowObject borrowObject}, {@link #returnObject returnObject} 027 * and {@link #invalidateObject invalidateObject}. 028 * </p> 029 * <p> 030 * Example of use: 031 * <pre style="border:solid thin; padding: 1ex;" 032 * > Object obj = <code style="color:#00C">null</code>; 033 * 034 * <code style="color:#00C">try</code> { 035 * obj = pool.borrowObject(); 036 * <code style="color:#00C">try</code> { 037 * <code style="color:#0C0">//...use the object...</code> 038 * } <code style="color:#00C">catch</code>(Exception e) { 039 * <code style="color:#0C0">// invalidate the object</code> 040 * pool.invalidateObject(obj); 041 * <code style="color:#0C0">// do not return the object to the pool twice</code> 042 * obj = <code style="color:#00C">null</code>; 043 * } <code style="color:#00C">finally</code> { 044 * <code style="color:#0C0">// make sure the object is returned to the pool</code> 045 * <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) { 046 * pool.returnObject(obj); 047 * } 048 * } 049 * } <code style="color:#00C">catch</code>(Exception e) { 050 * <code style="color:#0C0">// failed to borrow an object</code> 051 * }</pre> 052 * </p> 053 * 054 * <p>See {@link BaseObjectPool} for a simple base implementation.</p> 055 * 056 * @param <T> the type of objects held in this pool 057 * 058 * @author Rodney Waldhoff 059 * @author Sandy McArthur 060 * @version $Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $ 061 * @see PoolableObjectFactory 062 * @see ObjectPoolFactory 063 * @see KeyedObjectPool 064 * @see BaseObjectPool 065 * @since Pool 1.0 066 */ 067 public interface ObjectPool<T> { 068 /** 069 * Obtains an instance from this pool. 070 * <p> 071 * Instances returned from this method will have been either newly created with 072 * {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and 073 * have been activated with {@link PoolableObjectFactory#activateObject activateObject} and 074 * then validated with {@link PoolableObjectFactory#validateObject validateObject}. 075 * </p> 076 * <p> 077 * By contract, clients <strong>must</strong> return the borrowed instance using 078 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method 079 * as defined in an implementation or sub-interface. 080 * </p> 081 * <p> 082 * The behaviour of this method when the pool has been exhausted 083 * is not strictly specified (although it may be specified by implementations). 084 * Older versions of this method would return <code>null</code> to indicate exhaustion, 085 * newer versions are encouraged to throw a {@link NoSuchElementException}. 086 * </p> 087 * 088 * @return an instance from this pool. 089 * @throws IllegalStateException after {@link #close close} has been called on this pool. 090 * @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception. 091 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance. 092 */ 093 T borrowObject() throws Exception, NoSuchElementException, IllegalStateException; 094 095 /** 096 * Return an instance to the pool. 097 * By contract, <code>obj</code> <strong>must</strong> have been obtained 098 * using {@link #borrowObject() borrowObject} 099 * or a related method as defined in an implementation 100 * or sub-interface. 101 * 102 * @param obj a {@link #borrowObject borrowed} instance to be returned. 103 * @throws Exception 104 */ 105 void returnObject(T obj) throws Exception; 106 107 /** 108 * <p>Invalidates an object from the pool.</p> 109 * 110 * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained 111 * using {@link #borrowObject borrowObject} or a related method as defined in 112 * an implementation or sub-interface.</p> 113 * 114 * <p>This method should be used when an object that has been borrowed 115 * is determined (due to an exception or other problem) to be invalid.</p> 116 * 117 * @param obj a {@link #borrowObject borrowed} instance to be disposed. 118 * @throws Exception 119 */ 120 void invalidateObject(T obj) throws Exception; 121 122 /** 123 * Create an object using the {@link PoolableObjectFactory factory} or other 124 * implementation dependent mechanism, passivate it, and then place it in the idle object pool. 125 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects. 126 * (Optional operation). 127 * 128 * @throws Exception when {@link PoolableObjectFactory#makeObject} fails. 129 * @throws IllegalStateException after {@link #close} has been called on this pool. 130 * @throws UnsupportedOperationException when this pool cannot add new idle objects. 131 */ 132 void addObject() throws Exception, IllegalStateException, UnsupportedOperationException; 133 134 /** 135 * Return the number of instances 136 * currently idle in this pool (optional operation). 137 * This may be considered an approximation of the number 138 * of objects that can be {@link #borrowObject borrowed} 139 * without creating any new instances. 140 * Returns a negative value if this information is not available. 141 * 142 * @return the number of instances currently idle in this pool or a negative value if unsupported 143 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation 144 */ 145 int getNumIdle() throws UnsupportedOperationException; 146 147 /** 148 * Return the number of instances 149 * currently borrowed from this pool 150 * (optional operation). 151 * Returns a negative value if this information is not available. 152 * 153 * @return the number of instances currently borrowed from this pool or a negative value if unsupported 154 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation 155 */ 156 int getNumActive() throws UnsupportedOperationException; 157 158 /** 159 * Clears any objects sitting idle in the pool, releasing any 160 * associated resources (optional operation). 161 * Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}. 162 * 163 * @throws UnsupportedOperationException if this implementation does not support the operation 164 */ 165 void clear() throws Exception, UnsupportedOperationException; 166 167 /** 168 * Close this pool, and free any resources associated with it. 169 * <p> 170 * Calling {@link #addObject} or {@link #borrowObject} after invoking 171 * this method on a pool will cause them to throw an 172 * {@link IllegalStateException}. 173 * </p> 174 * 175 * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed. 176 */ 177 void close() throws Exception; 178 179 /** 180 * Sets the {@link PoolableObjectFactory factory} this pool uses 181 * to create new instances (optional operation). Trying to change 182 * the <code>factory</code> after a pool has been used will frequently 183 * throw an {@link UnsupportedOperationException}. It is up to the pool 184 * implementation to determine when it is acceptable to call this method. 185 * 186 * @param factory the {@link PoolableObjectFactory} used to create new instances. 187 * @throws IllegalStateException when the factory cannot be set at this time 188 * @throws UnsupportedOperationException if this implementation does not support the operation 189 * @deprecated to be removed in pool 2.0 190 */ 191 @Deprecated 192 void setFactory(PoolableObjectFactory<T> factory) throws IllegalStateException, UnsupportedOperationException; 193 }