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 pooling simple interface. 024 * <p> 025 * Example of use: 026 * </p> 027 * <pre style="border:solid thin; padding: 1ex;" 028 * > Object obj = <code style="color:#00C">null</code>; 029 * 030 * <code style="color:#00C">try</code> { 031 * obj = pool.borrowObject(); 032 * <code style="color:#00C">try</code> { 033 * <code style="color:#0C0">//...use the object...</code> 034 * } <code style="color:#00C">catch</code>(Exception e) { 035 * <code style="color:#0C0">// invalidate the object</code> 036 * pool.invalidateObject(obj); 037 * <code style="color:#0C0">// do not return the object to the pool twice</code> 038 * obj = <code style="color:#00C">null</code>; 039 * } <code style="color:#00C">finally</code> { 040 * <code style="color:#0C0">// make sure the object is returned to the pool</code> 041 * <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) { 042 * pool.returnObject(obj); 043 * } 044 * } 045 * } <code style="color:#00C">catch</code>(Exception e) { 046 * <code style="color:#0C0">// failed to borrow an object</code> 047 * }</pre> 048 * <p> 049 * See {@link BaseObjectPool} for a simple base implementation. 050 * </p> 051 * 052 * @param <T> Type of element pooled in this pool. 053 * 054 * @see PooledObjectFactory 055 * @see KeyedObjectPool 056 * @see BaseObjectPool 057 * 058 * @since 2.0 059 */ 060public interface ObjectPool<T> extends Closeable { 061 062 /** 063 * Creates an object using the {@link PooledObjectFactory factory} or other 064 * implementation dependent mechanism, passivate it, and then place it in 065 * the idle object pool. <code>addObject</code> is useful for "pre-loading" 066 * a pool with idle objects. (Optional operation). 067 * 068 * @throws Exception 069 * when {@link PooledObjectFactory#makeObject} fails. 070 * @throws IllegalStateException 071 * after {@link #close} has been called on this pool. 072 * @throws UnsupportedOperationException 073 * when this pool cannot add new idle objects. 074 */ 075 void addObject() throws Exception, IllegalStateException, 076 UnsupportedOperationException; 077 078 /** 079 * Calls {@link ObjectPool#addObject()} <code>count</code> 080 * number of times. 081 * 082 * @param count 083 * the number of idle objects to add. 084 * @throws Exception 085 * when {@link ObjectPool#addObject()} fails. 086 * @since 2.8.0 087 */ 088 default void addObjects(final int count) throws Exception { 089 for (int i = 0; i < count; i++) { 090 addObject(); 091 } 092 } 093 094 /** 095 * Obtains an instance from this pool. 096 * <p> 097 * Instances returned from this method will have been either newly created 098 * with {@link PooledObjectFactory#makeObject} or will be a previously 099 * idle object and have been activated with 100 * {@link PooledObjectFactory#activateObject} and then validated with 101 * {@link PooledObjectFactory#validateObject}. 102 * </p> 103 * <p> 104 * By contract, clients <strong>must</strong> return the borrowed instance 105 * using {@link #returnObject}, {@link #invalidateObject}, or a related 106 * method as defined in an implementation or sub-interface. 107 * </p> 108 * <p> 109 * The behaviour of this method when the pool has been exhausted 110 * is not strictly specified (although it may be specified by 111 * implementations). 112 * </p> 113 * 114 * @return an instance from this pool. 115 * 116 * @throws IllegalStateException 117 * after {@link #close close} has been called on this pool. 118 * @throws Exception 119 * when {@link PooledObjectFactory#makeObject} throws an 120 * exception. 121 * @throws NoSuchElementException 122 * when the pool is exhausted and cannot or will not return 123 * another instance. 124 */ 125 T borrowObject() throws Exception, NoSuchElementException, 126 IllegalStateException; 127 128 /** 129 * Clears any objects sitting idle in the pool, releasing any associated 130 * resources (optional operation). Idle objects cleared must be 131 * {@link PooledObjectFactory#destroyObject(PooledObject)}. 132 * 133 * @throws UnsupportedOperationException 134 * if this implementation does not support the operation 135 * 136 * @throws Exception if the pool cannot be cleared 137 */ 138 void clear() throws Exception, UnsupportedOperationException; 139 140 /** 141 * Closes this pool, and free any resources associated with it. 142 * <p> 143 * Calling {@link #addObject} or {@link #borrowObject} after invoking this 144 * method on a pool will cause them to throw an {@link IllegalStateException}. 145 * </p> 146 * <p> 147 * Implementations should silently fail if not all resources can be freed. 148 * </p> 149 */ 150 @Override 151 void close(); 152 153 /** 154 * Returns the number of instances currently borrowed from this pool. Returns 155 * a negative value if this information is not available. 156 * @return the number of instances currently borrowed from this pool. 157 */ 158 int getNumActive(); 159 160 /** 161 * Returns the number of instances currently idle in this pool. This may be 162 * considered an approximation of the number of objects that can be 163 * {@link #borrowObject borrowed} without creating any new instances. 164 * Returns a negative value if this information is not available. 165 * @return the number of instances currently idle in this pool. 166 */ 167 int getNumIdle(); 168 169 /** 170 * Invalidates an object from the pool. 171 * <p> 172 * By contract, <code>obj</code> <strong>must</strong> have been obtained 173 * using {@link #borrowObject} or a related method as defined in an 174 * implementation or sub-interface. 175 * </p> 176 * <p> 177 * This method should be used when an object that has been borrowed is 178 * determined (due to an exception or other problem) to be invalid. 179 * </p> 180 * 181 * @param obj a {@link #borrowObject borrowed} instance to be disposed. 182 * 183 * @throws Exception if the instance cannot be invalidated 184 */ 185 void invalidateObject(T obj) throws Exception; 186 187 /** 188 * Returns an instance to the pool. By contract, <code>obj</code> 189 * <strong>must</strong> have been obtained using {@link #borrowObject()} or 190 * a related method as defined in an implementation or sub-interface. 191 * 192 * @param obj a {@link #borrowObject borrowed} instance to be returned. 193 * 194 * @throws IllegalStateException 195 * if an attempt is made to return an object to the pool that 196 * is in any state other than allocated (i.e. borrowed). 197 * Attempting to return an object more than once or attempting 198 * to return an object that was never borrowed from the pool 199 * will trigger this exception. 200 * 201 * @throws Exception if an instance cannot be returned to the pool 202 */ 203 void returnObject(T obj) throws Exception; 204}