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 019import java.io.Closeable; 020import java.util.NoSuchElementException; 021 022/** 023 * A "keyed" pooling interface. 024 * <p> 025 * A keyed pool maintains a pool of instances for each key value. 026 * </p> 027 * <p> 028 * Example of use: 029 * </p> 030 * <pre style="border:solid thin; padding: 1ex;" 031 * > Object obj = <code style="color:#00C">null</code>; 032 * Object key = <code style="color:#C00">"Key"</code>; 033 * 034 * <code style="color:#00C">try</code> { 035 * obj = pool.borrowObject(key); 036 * <code style="color:#0C0">//...use the object...</code> 037 * } <code style="color:#00C">catch</code>(Exception e) { 038 * <code style="color:#0C0">// invalidate the object</code> 039 * pool.invalidateObject(key, obj); 040 * <code style="color:#0C0">// do not return the object to the pool twice</code> 041 * obj = <code style="color:#00C">null</code>; 042 * } <code style="color:#00C">finally</code> { 043 * <code style="color:#0C0">// make sure the object is returned to the pool</code> 044 * <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) { 045 * pool.returnObject(key, obj); 046 * } 047 * }</pre> 048 * <p> 049 * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most 050 * one instance per key value, or may choose to maintain a pool of instances 051 * for each key (essentially creating a {@link java.util.Map Map} of 052 * {@link ObjectPool pools}). 053 * </p> 054 * <p> 055 * See {@link org.apache.commons.pool2.impl.GenericKeyedObjectPool 056 * GenericKeyedObjectPool} for an implementation. 057 * </p> 058 * 059 * @param <K> The type of keys maintained by this pool. 060 * @param <V> Type of element pooled in this pool. 061 * 062 * @see KeyedPooledObjectFactory 063 * @see ObjectPool 064 * @see org.apache.commons.pool2.impl.GenericKeyedObjectPool GenericKeyedObjectPool 065 * 066 * @since 2.0 067 */ 068public interface KeyedObjectPool<K, V> extends Closeable { 069 /** 070 * Obtains an instance from this pool for the specified <code>key</code>. 071 * <p> 072 * Instances returned from this method will have been either newly created 073 * with {@link KeyedPooledObjectFactory#makeObject makeObject} or will be 074 * a previously idle object and have been activated with 075 * {@link KeyedPooledObjectFactory#activateObject activateObject} and then 076 * (optionally) validated with 077 * {@link KeyedPooledObjectFactory#validateObject validateObject}. 078 * </p> 079 * <p> 080 * By contract, clients <strong>must</strong> return the borrowed object 081 * using {@link #returnObject returnObject}, 082 * {@link #invalidateObject invalidateObject}, or a related method as 083 * defined in an implementation or sub-interface, using a <code>key</code> 084 * that is {@link Object#equals equivalent} to the one used to borrow the 085 * instance in the first place. 086 * </p> 087 * <p> 088 * The behaviour of this method when the pool has been exhausted is not 089 * strictly specified (although it may be specified by implementations). 090 * </p> 091 * 092 * @param key the key used to obtain the object 093 * 094 * @return an instance from this pool. 095 * 096 * @throws IllegalStateException 097 * after {@link #close close} has been called on this pool 098 * @throws Exception 099 * when {@link KeyedPooledObjectFactory#makeObject 100 * makeObject} throws an exception 101 * @throws NoSuchElementException 102 * when the pool is exhausted and cannot or will not return 103 * another instance 104 */ 105 V borrowObject(K key) throws Exception, NoSuchElementException, IllegalStateException; 106 107 /** 108 * Return an instance to the pool. By contract, <code>obj</code> 109 * <strong>must</strong> have been obtained using 110 * {@link #borrowObject borrowObject} or a related method as defined in an 111 * implementation or sub-interface using a <code>key</code> that is 112 * equivalent to the one used to borrow the instance in the first place. 113 * 114 * @param key the key used to obtain the object 115 * @param obj a {@link #borrowObject borrowed} instance to be returned. 116 * 117 * @throws IllegalStateException 118 * if an attempt is made to return an object to the pool that 119 * is in any state other than allocated (i.e. borrowed). 120 * Attempting to return an object more than once or attempting 121 * to return an object that was never borrowed from the pool 122 * will trigger this exception. 123 * 124 * @throws Exception if an instance cannot be returned to the pool 125 */ 126 void returnObject(K key, V obj) throws Exception; 127 128 /** 129 * Invalidates an object from the pool. 130 * <p> 131 * By contract, <code>obj</code> <strong>must</strong> have been obtained 132 * using {@link #borrowObject borrowObject} or a related method as defined 133 * in an implementation or sub-interface using a <code>key</code> that is 134 * equivalent to the one used to borrow the <code>Object</code> in the first 135 * place. 136 * </p> 137 * <p> 138 * This method should be used when an object that has been borrowed is 139 * determined (due to an exception or other problem) to be invalid. 140 * </p> 141 * 142 * @param key the key used to obtain the object 143 * @param obj a {@link #borrowObject borrowed} instance to be returned. 144 * 145 * @throws Exception if the instance cannot be invalidated 146 */ 147 void invalidateObject(K key, V obj) throws Exception; 148 149 /** 150 * Create an object using the {@link KeyedPooledObjectFactory factory} or 151 * other implementation dependent mechanism, passivate it, and then place it 152 * in the idle object pool. <code>addObject</code> is useful for 153 * "pre-loading" a pool with idle objects (Optional operation). 154 * 155 * @param key the key a new instance should be added to 156 * 157 * @throws Exception 158 * when {@link KeyedPooledObjectFactory#makeObject} fails. 159 * @throws IllegalStateException 160 * after {@link #close} has been called on this pool. 161 * @throws UnsupportedOperationException 162 * when this pool cannot add new idle objects. 163 */ 164 void addObject(K key) throws Exception, IllegalStateException, 165 UnsupportedOperationException; 166 167 /** 168 * Returns the number of instances corresponding to the given 169 * <code>key</code> currently idle in this pool. Returns a negative value if 170 * this information is not available. 171 * 172 * @param key the key to query 173 * @return the number of instances corresponding to the given 174 * <code>key</code> currently idle in this pool. 175 */ 176 int getNumIdle(K key); 177 178 /** 179 * Returns the number of instances currently borrowed from but not yet 180 * returned to the pool corresponding to the given <code>key</code>. 181 * Returns a negative value if this information is not available. 182 * 183 * @param key the key to query 184 * @return the number of instances currently borrowed from but not yet 185 * returned to the pool corresponding to the given <code>key</code>. 186= */ 187 int getNumActive(K key); 188 189 /** 190 * Returns the total number of instances currently idle in this pool. 191 * Returns a negative value if this information is not available. 192 * @return the total number of instances currently idle in this pool. 193 = */ 194 int getNumIdle(); 195 196 /** 197 * Returns the total number of instances currently borrowed from this pool but 198 * not yet returned. Returns a negative value if this information is not 199 * available. 200 * @return the total number of instances currently borrowed from this pool but 201 * not yet returned. 202 */ 203 int getNumActive(); 204 205 /** 206 * Clears the pool, removing all pooled instances (optional operation). 207 * 208 * @throws UnsupportedOperationException when this implementation doesn't 209 * support the operation 210 * 211 * @throws Exception if the pool cannot be cleared 212 */ 213 void clear() throws Exception, UnsupportedOperationException; 214 215 /** 216 * Clears the specified pool, removing all pooled instances corresponding to 217 * the given <code>key</code> (optional operation). 218 * 219 * @param key the key to clear 220 * 221 * @throws UnsupportedOperationException when this implementation doesn't 222 * support the operation 223 * 224 * @throws Exception if the key cannot be cleared 225 */ 226 void clear(K key) throws Exception, UnsupportedOperationException; 227 228 /** 229 * Close this pool, and free any resources associated with it. 230 * <p> 231 * Calling {@link #addObject addObject} or 232 * {@link #borrowObject borrowObject} after invoking this method on a pool 233 * will cause them to throw an {@link IllegalStateException}. 234 * </p> 235 * <p> 236 * Implementations should silently fail if not all resources can be freed. 237 * </p> 238 */ 239 @Override 240 void close(); 241}