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 "keyed" pooling interface.
024 * <p>
025 * A keyed pool pools instances of multiple types. Each
026 * type may be accessed using an arbitrary key.
027 * </p>
028 * <p>
029 * Example of use:
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 * <p>
050 * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most
051 * one instance per key value, or may choose to maintain a pool of instances
052 * for each key (essentially creating a {@link java.util.Map Map} of
053 * {@link ObjectPool pools}).
054 * </p>
055 *
056 * <p>See {@link BaseKeyedObjectPool} for a simple base implementation.</p>
057 *
058 * @author Rodney Waldhoff
059 * @author Sandy McArthur
060 * @version $Revision: 778480 $ $Date: 2009-05-25 15:34:55 -0400 (Mon, 25 May 2009) $
061 * @see KeyedPoolableObjectFactory
062 * @see KeyedObjectPoolFactory
063 * @see ObjectPool
064 * @see BaseKeyedObjectPool
065 * @since Pool 1.0
066 */
067 public interface KeyedObjectPool {
068 /**
069 * Obtains an instance from this pool for the specified <code>key</code>.
070 * <p>
071 * Instances returned from this method will have been either newly created with
072 * {@link KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
073 * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and
074 * then validated with {@link KeyedPoolableObjectFactory#validateObject validateObject}.
075 * <p>
076 * By contract, clients <strong>must</strong> return the borrowed object using
077 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
078 * as defined in an implementation or sub-interface,
079 * using a <code>key</code> that is {@link Object#equals equivalent} to the one used to
080 * borrow the instance in the first place.
081 * <p>
082 * The behaviour of this method when the pool has been exhausted
083 * is not strictly specified (although it may be specified by implementations).
084 * Older versions of this method would return <code>null</code> to indicate exhaustion,
085 * newer versions are encouraged to throw a {@link NoSuchElementException}.
086 *
087 * @param key the key used to obtain the object
088 * @return an instance from this pool.
089 * @throws IllegalStateException after {@link #close close} has been called on this pool
090 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject makeObject} throws an exception
091 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance
092 */
093 Object borrowObject(Object key) throws Exception, NoSuchElementException, IllegalStateException;
094
095 /**
096 * Return an instance to the pool.
097 * By contract, <code>obj</code> <strong>must</strong> have been obtained
098 * using {@link #borrowObject borrowObject}
099 * or a related method as defined in an implementation
100 * or sub-interface
101 * using a <code>key</code> that is equivalent to the one used to
102 * borrow the instance in the first place.
103 *
104 * @param key the key used to obtain the object
105 * @param obj a {@link #borrowObject borrowed} instance to be returned.
106 * @throws Exception
107 */
108 void returnObject(Object key, Object obj) throws Exception;
109
110 /**
111 * Invalidates an object from the pool
112 * By contract, <code>obj</code> <strong>must</strong> have been obtained
113 * using {@link #borrowObject borrowObject}
114 * or a related method as defined in an implementation
115 * or sub-interface
116 * using a <code>key</code> that is equivalent to the one used to
117 * borrow the <code>Object</code> in the first place.
118 * <p>
119 * This method should be used when an object that has been borrowed
120 * is determined (due to an exception or other problem) to be invalid.
121 * </p>
122 *
123 * @param key the key used to obtain the object
124 * @param obj a {@link #borrowObject borrowed} instance to be returned.
125 * @throws Exception
126 */
127 void invalidateObject(Object key, Object obj) throws Exception;
128
129 /**
130 * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
131 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
132 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
133 * (Optional operation).
134 *
135 * @param key the key a new instance should be added to
136 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
137 * @throws IllegalStateException after {@link #close} has been called on this pool.
138 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
139 */
140 void addObject(Object key) throws Exception, IllegalStateException, UnsupportedOperationException;
141
142 /**
143 * Returns the number of instances
144 * corresponding to the given <code>key</code>
145 * currently idle in this pool (optional operation).
146 * Returns a negative value if this information is not available.
147 *
148 * @param key the key to query
149 * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
150 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
151 */
152 int getNumIdle(Object key) throws UnsupportedOperationException;
153
154 /**
155 * Returns the number of instances
156 * currently borrowed from but not yet returned
157 * to the pool corresponding to the
158 * given <code>key</code> (optional operation).
159 * Returns a negative value if this information is not available.
160 *
161 * @param key the key to query
162 * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
163 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
164 */
165 int getNumActive(Object key) throws UnsupportedOperationException;
166
167 /**
168 * Returns the total number of instances
169 * currently idle in this pool (optional operation).
170 * Returns a negative value if this information is not available.
171 *
172 * @return the total number of instances currently idle in this pool or a negative value if unsupported
173 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
174 */
175 int getNumIdle() throws UnsupportedOperationException;
176
177 /**
178 * Returns the total number of instances
179 * current borrowed from this pool but not
180 * yet returned (optional operation).
181 * Returns a negative value if this information is not available.
182 *
183 * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
184 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
185 */
186 int getNumActive() throws UnsupportedOperationException;
187
188 /**
189 * Clears the pool, removing all pooled instances (optional operation).
190 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
191 *
192 * @throws UnsupportedOperationException when this implementation doesn't support the operation
193 */
194 void clear() throws Exception, UnsupportedOperationException;
195
196 /**
197 * Clears the specified pool, removing all
198 * pooled instances corresponding to
199 * the given <code>key</code> (optional operation).
200 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
201 *
202 * @param key the key to clear
203 * @throws UnsupportedOperationException when this implementation doesn't support the operation
204 */
205 void clear(Object key) throws Exception, UnsupportedOperationException;
206
207 /**
208 * Close this pool, and free any resources associated with it.
209 * <p>
210 * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
211 * this method on a pool will cause them to throw an {@link IllegalStateException}.
212 * </p>
213 *
214 * @throws Exception
215 */
216 void close() throws Exception;
217
218 /**
219 * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
220 * to create new instances (optional operation).
221 * Trying to change the <code>factory</code> after a pool has been used will frequently
222 * throw an {@link UnsupportedOperationException}. It is up to the pool
223 * implementation to determine when it is acceptable to call this method.
224 *
225 * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
226 * @throws IllegalStateException when the factory cannot be set at this time
227 * @throws UnsupportedOperationException when this implementation doesn't support the operation
228 */
229 void setFactory(KeyedPoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
230 }