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 * @author Rodney Waldhoff
057 * @author Sandy McArthur
058 * @version $Revision: 962893 $ $Date: 2010-07-10 10:37:27 -0700 (Sat, 10 Jul 2010) $
059 * @see PoolableObjectFactory
060 * @see ObjectPoolFactory
061 * @see KeyedObjectPool
062 * @see BaseObjectPool
063 * @since Pool 1.0
064 */
065 public interface ObjectPool {
066 /**
067 * Obtains an instance from this pool.
068 * <p>
069 * Instances returned from this method will have been either newly created with
070 * {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
071 * have been activated with {@link PoolableObjectFactory#activateObject activateObject} and
072 * then validated with {@link PoolableObjectFactory#validateObject validateObject}.
073 * </p>
074 * <p>
075 * By contract, clients <strong>must</strong> return the borrowed instance using
076 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
077 * as defined in an implementation or sub-interface.
078 * </p>
079 * <p>
080 * The behaviour of this method when the pool has been exhausted
081 * is not strictly specified (although it may be specified by implementations).
082 * Older versions of this method would return <code>null</code> to indicate exhaustion,
083 * newer versions are encouraged to throw a {@link NoSuchElementException}.
084 * </p>
085 *
086 * @return an instance from this pool.
087 * @throws IllegalStateException after {@link #close close} has been called on this pool.
088 * @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception.
089 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance.
090 */
091 Object borrowObject() throws Exception, NoSuchElementException, IllegalStateException;
092
093 /**
094 * Return an instance to the pool.
095 * By contract, <code>obj</code> <strong>must</strong> have been obtained
096 * using {@link #borrowObject() borrowObject}
097 * or a related method as defined in an implementation
098 * or sub-interface.
099 *
100 * @param obj a {@link #borrowObject borrowed} instance to be returned.
101 * @throws Exception
102 */
103 void returnObject(Object obj) throws Exception;
104
105 /**
106 * <p>Invalidates an object from the pool.</p>
107 *
108 * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
109 * using {@link #borrowObject borrowObject} or a related method as defined in
110 * an implementation or sub-interface.</p>
111 *
112 * <p>This method should be used when an object that has been borrowed
113 * is determined (due to an exception or other problem) to be invalid.</p>
114 *
115 * @param obj a {@link #borrowObject borrowed} instance to be disposed.
116 * @throws Exception
117 */
118 void invalidateObject(Object obj) throws Exception;
119
120 /**
121 * Create an object using the {@link PoolableObjectFactory factory} or other
122 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
123 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
124 * (Optional operation).
125 *
126 * @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
127 * @throws IllegalStateException after {@link #close} has been called on this pool.
128 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
129 */
130 void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;
131
132 /**
133 * Return the number of instances
134 * currently idle in this pool (optional operation).
135 * This may be considered an approximation of the number
136 * of objects that can be {@link #borrowObject borrowed}
137 * without creating any new instances.
138 * Returns a negative value if this information is not available.
139 *
140 * @return the number of instances currently idle in this pool or a negative value if unsupported
141 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
142 */
143 int getNumIdle() throws UnsupportedOperationException;
144
145 /**
146 * Return the number of instances
147 * currently borrowed from this pool
148 * (optional operation).
149 * Returns a negative value if this information is not available.
150 *
151 * @return the number of instances currently borrowed from this pool or a negative value if unsupported
152 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
153 */
154 int getNumActive() throws UnsupportedOperationException;
155
156 /**
157 * Clears any objects sitting idle in the pool, releasing any
158 * associated resources (optional operation).
159 * Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
160 *
161 * @throws UnsupportedOperationException if this implementation does not support the operation
162 */
163 void clear() throws Exception, UnsupportedOperationException;
164
165 /**
166 * Close this pool, and free any resources associated with it.
167 * <p>
168 * Calling {@link #addObject} or {@link #borrowObject} after invoking
169 * this method on a pool will cause them to throw an
170 * {@link IllegalStateException}.
171 * </p>
172 *
173 * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
174 */
175 void close() throws Exception;
176
177 /**
178 * Sets the {@link PoolableObjectFactory factory} this pool uses
179 * to create new instances (optional operation). Trying to change
180 * the <code>factory</code> after a pool has been used will frequently
181 * throw an {@link UnsupportedOperationException}. It is up to the pool
182 * implementation to determine when it is acceptable to call this method.
183 *
184 * @param factory the {@link PoolableObjectFactory} used to create new instances.
185 * @throws IllegalStateException when the factory cannot be set at this time
186 * @throws UnsupportedOperationException if this implementation does not support the operation
187 * @deprecated to be removed in pool 2.0
188 */
189 void setFactory(PoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
190 }