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 * Obtains an instance from this pool. 064 * <p> 065 * Instances returned from this method will have been either newly created 066 * with {@link PooledObjectFactory#makeObject} or will be a previously 067 * idle object and have been activated with 068 * {@link PooledObjectFactory#activateObject} and then validated with 069 * {@link PooledObjectFactory#validateObject}. 070 * </p> 071 * <p> 072 * By contract, clients <strong>must</strong> return the borrowed instance 073 * using {@link #returnObject}, {@link #invalidateObject}, or a related 074 * method as defined in an implementation or sub-interface. 075 * </p> 076 * <p> 077 * The behaviour of this method when the pool has been exhausted 078 * is not strictly specified (although it may be specified by 079 * implementations). 080 * </p> 081 * 082 * @return an instance from this pool. 083 * 084 * @throws IllegalStateException 085 * after {@link #close close} has been called on this pool. 086 * @throws Exception 087 * when {@link PooledObjectFactory#makeObject} throws an 088 * exception. 089 * @throws NoSuchElementException 090 * when the pool is exhausted and cannot or will not return 091 * another instance. 092 */ 093 T borrowObject() throws Exception, NoSuchElementException, 094 IllegalStateException; 095 096 /** 097 * Returns an instance to the pool. By contract, <code>obj</code> 098 * <strong>must</strong> have been obtained using {@link #borrowObject()} or 099 * a related method as defined in an implementation or sub-interface. 100 * 101 * @param obj a {@link #borrowObject borrowed} instance to be returned. 102 * 103 * @throws IllegalStateException 104 * if an attempt is made to return an object to the pool that 105 * is in any state other than allocated (i.e. borrowed). 106 * Attempting to return an object more than once or attempting 107 * to return an object that was never borrowed from the pool 108 * will trigger this exception. 109 * 110 * @throws Exception if an instance cannot be returned to the pool 111 */ 112 void returnObject(T obj) throws Exception; 113 114 /** 115 * Invalidates an object from the pool. 116 * <p> 117 * By contract, <code>obj</code> <strong>must</strong> have been obtained 118 * using {@link #borrowObject} or a related method as defined in an 119 * implementation or sub-interface. 120 * </p> 121 * <p> 122 * This method should be used when an object that has been borrowed is 123 * determined (due to an exception or other problem) to be invalid. 124 * </p> 125 * 126 * @param obj a {@link #borrowObject borrowed} instance to be disposed. 127 * 128 * @throws Exception if the instance cannot be invalidated 129 */ 130 void invalidateObject(T obj) throws Exception; 131 132 /** 133 * Creates an object using the {@link PooledObjectFactory factory} or other 134 * implementation dependent mechanism, passivate it, and then place it in 135 * the idle object pool. <code>addObject</code> is useful for "pre-loading" 136 * a pool with idle objects. (Optional operation). 137 * 138 * @throws Exception 139 * when {@link PooledObjectFactory#makeObject} fails. 140 * @throws IllegalStateException 141 * after {@link #close} has been called on this pool. 142 * @throws UnsupportedOperationException 143 * when this pool cannot add new idle objects. 144 */ 145 void addObject() throws Exception, IllegalStateException, 146 UnsupportedOperationException; 147 148 /** 149 * Returns the number of instances currently idle in this pool. This may be 150 * considered an approximation of the number of objects that can be 151 * {@link #borrowObject borrowed} without creating any new instances. 152 * Returns a negative value if this information is not available. 153 * @return the number of instances currently idle in this pool. 154 */ 155 int getNumIdle(); 156 157 /** 158 * Returns the number of instances currently borrowed from this pool. Returns 159 * a negative value if this information is not available. 160 * @return the number of instances currently borrowed from this pool. 161 */ 162 int getNumActive(); 163 164 /** 165 * Clears any objects sitting idle in the pool, releasing any associated 166 * resources (optional operation). Idle objects cleared must be 167 * {@link PooledObjectFactory#destroyObject(PooledObject)}. 168 * 169 * @throws UnsupportedOperationException 170 * if this implementation does not support the operation 171 * 172 * @throws Exception if the pool cannot be cleared 173 */ 174 void clear() throws Exception, UnsupportedOperationException; 175 176 /** 177 * Closes this pool, and free any resources associated with it. 178 * <p> 179 * Calling {@link #addObject} or {@link #borrowObject} after invoking this 180 * method on a pool will cause them to throw an {@link IllegalStateException}. 181 * </p> 182 * <p> 183 * Implementations should silently fail if not all resources can be freed. 184 * </p> 185 */ 186 @Override 187 void close(); 188}