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:#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(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(obj);
046 * }
047 * }</pre>
048 * </p>
049 *
050 * <p>See {@link BaseObjectPool} for a simple base implementation.</p>
051 *
052 * @author Rodney Waldhoff
053 * @author Sandy McArthur
054 * @version $Revision: 778007 $ $Date: 2009-05-23 15:57:11 -0400 (Sat, 23 May 2009) $
055 * @see PoolableObjectFactory
056 * @see ObjectPoolFactory
057 * @see KeyedObjectPool
058 * @see BaseObjectPool
059 * @since Pool 1.0
060 */
061 public interface ObjectPool {
062 /**
063 * Obtains an instance from this pool.
064 * <p>
065 * Instances returned from this method will have been either newly created with
066 * {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
067 * have been activated with {@link PoolableObjectFactory#activateObject activateObject} and
068 * then validated with {@link PoolableObjectFactory#validateObject validateObject}.
069 * </p>
070 * <p>
071 * By contract, clients <strong>must</strong> return the borrowed instance using
072 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
073 * as defined in an implementation or sub-interface.
074 * </p>
075 * <p>
076 * The behaviour of this method when the pool has been exhausted
077 * is not strictly specified (although it may be specified by implementations).
078 * Older versions of this method would return <code>null</code> to indicate exhaustion,
079 * newer versions are encouraged to throw a {@link NoSuchElementException}.
080 * </p>
081 *
082 * @return an instance from this pool.
083 * @throws IllegalStateException after {@link #close close} has been called on this pool.
084 * @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception.
085 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance.
086 */
087 Object borrowObject() throws Exception, NoSuchElementException, IllegalStateException;
088
089 /**
090 * Return an instance to the pool.
091 * By contract, <code>obj</code> <strong>must</strong> have been obtained
092 * using {@link #borrowObject() borrowObject}
093 * or a related method as defined in an implementation
094 * or sub-interface.
095 *
096 * @param obj a {@link #borrowObject borrowed} instance to be returned.
097 * @throws Exception
098 */
099 void returnObject(Object obj) throws Exception;
100
101 /**
102 * Invalidates an object from the pool.
103 * By contract, <code>obj</code> <strong>must</strong> have been obtained
104 * using {@link #borrowObject borrowObject}
105 * or a related method as defined in an implementation
106 * or sub-interface.
107 * <p>
108 * This method should be used when an object that has been borrowed
109 * is determined (due to an exception or other problem) to be invalid.
110 * </p>
111 *
112 * @param obj a {@link #borrowObject borrowed} instance to be disposed.
113 * @throws Exception
114 */
115 void invalidateObject(Object obj) throws Exception;
116
117 /**
118 * Create an object using the {@link PoolableObjectFactory factory} or other
119 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
120 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
121 * (Optional operation).
122 *
123 * @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
124 * @throws IllegalStateException after {@link #close} has been called on this pool.
125 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
126 */
127 void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;
128
129 /**
130 * Return the number of instances
131 * currently idle in this pool (optional operation).
132 * This may be considered an approximation of the number
133 * of objects that can be {@link #borrowObject borrowed}
134 * without creating any new instances.
135 * Returns a negative value if this information is not available.
136 *
137 * @return the number of instances currently idle in this pool or a negative value if unsupported
138 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
139 */
140 int getNumIdle() throws UnsupportedOperationException;
141
142 /**
143 * Return the number of instances
144 * currently borrowed from this pool
145 * (optional operation).
146 * Returns a negative value if this information is not available.
147 *
148 * @return the number of instances currently borrowed from this pool or a negative value if unsupported
149 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
150 */
151 int getNumActive() throws UnsupportedOperationException;
152
153 /**
154 * Clears any objects sitting idle in the pool, releasing any
155 * associated resources (optional operation).
156 * Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
157 *
158 * @throws UnsupportedOperationException if this implementation does not support the operation
159 */
160 void clear() throws Exception, UnsupportedOperationException;
161
162 /**
163 * Close this pool, and free any resources associated with it.
164 * <p>
165 * Calling {@link #addObject} or {@link #borrowObject} after invoking
166 * this method on a pool will cause them to throw an
167 * {@link IllegalStateException}.
168 * </p>
169 *
170 * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
171 */
172 void close() throws Exception;
173
174 /**
175 * Sets the {@link PoolableObjectFactory factory} this pool uses
176 * to create new instances (optional operation). Trying to change
177 * the <code>factory</code> after a pool has been used will frequently
178 * throw an {@link UnsupportedOperationException}. It is up to the pool
179 * implementation to determine when it is acceptable to call this method.
180 *
181 * @param factory the {@link PoolableObjectFactory} used to create new instances.
182 * @throws IllegalStateException when the factory cannot be set at this time
183 * @throws UnsupportedOperationException if this implementation does not support the operation
184 */
185 void setFactory(PoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
186 }