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 * @param <K> the type of keys in this pool
059 * @param <V> the type of objects held in this pool
060 *
061 * @author Rodney Waldhoff
062 * @author Sandy McArthur
063 * @version $Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $
064 * @see KeyedPoolableObjectFactory
065 * @see KeyedObjectPoolFactory
066 * @see ObjectPool
067 * @see BaseKeyedObjectPool
068 * @since Pool 1.0
069 */
070 public interface KeyedObjectPool<K, V> {
071 /**
072 * Obtains an instance from this pool for the specified <code>key</code>.
073 * <p>
074 * Instances returned from this method will have been either newly created with
075 * {@link KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
076 * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and
077 * then validated with {@link KeyedPoolableObjectFactory#validateObject validateObject}.
078 * <p>
079 * By contract, clients <strong>must</strong> return the borrowed object using
080 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
081 * as defined in an implementation or sub-interface,
082 * using a <code>key</code> that is {@link Object#equals equivalent} to the one used to
083 * borrow the instance in the first place.
084 * <p>
085 * The behaviour of this method when the pool has been exhausted
086 * is not strictly specified (although it may be specified by implementations).
087 * Older versions of this method would return <code>null</code> to indicate exhaustion,
088 * newer versions are encouraged to throw a {@link NoSuchElementException}.
089 *
090 * @param key the key used to obtain the object
091 * @return an instance from this pool.
092 * @throws IllegalStateException after {@link #close close} has been called on this pool
093 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject makeObject} throws an exception
094 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance
095 */
096 V borrowObject(K key) throws Exception, NoSuchElementException, IllegalStateException;
097
098 /**
099 * Return an instance to the pool.
100 * By contract, <code>obj</code> <strong>must</strong> have been obtained
101 * using {@link #borrowObject borrowObject}
102 * or a related method as defined in an implementation
103 * or sub-interface
104 * using a <code>key</code> that is equivalent to the one used to
105 * borrow the instance in the first place.
106 *
107 * @param key the key used to obtain the object
108 * @param obj a {@link #borrowObject borrowed} instance to be returned.
109 * @throws Exception
110 */
111 void returnObject(K key, V obj) throws Exception;
112
113 /**
114 * <p>Invalidates an object from the pool.</p>
115 *
116 * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
117 * using {@link #borrowObject borrowObject} or a related method as defined
118 * in an implementation or sub-interface using a <code>key</code> that is
119 * equivalent to the one used to borrow the <code>Object</code> in the first place.</p>
120 *
121 * <p>This method should be used when an object that has been borrowed
122 * is determined (due to an exception or other problem) to be invalid.</p>
123 *
124 * @param key the key used to obtain the object
125 * @param obj a {@link #borrowObject borrowed} instance to be returned.
126 * @throws Exception
127 */
128 void invalidateObject(K key, V obj) throws Exception;
129
130 /**
131 * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
132 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
133 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
134 * (Optional operation).
135 *
136 * @param key the key a new instance should be added to
137 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
138 * @throws IllegalStateException after {@link #close} has been called on this pool.
139 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
140 */
141 void addObject(K key) throws Exception, IllegalStateException, UnsupportedOperationException;
142
143 /**
144 * Returns the number of instances
145 * corresponding to the given <code>key</code>
146 * currently idle in this pool (optional operation).
147 * Returns a negative value if this information is not available.
148 *
149 * @param key the key to query
150 * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
151 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
152 */
153 int getNumIdle(K key) throws UnsupportedOperationException;
154
155 /**
156 * Returns the number of instances
157 * currently borrowed from but not yet returned
158 * to the pool corresponding to the
159 * given <code>key</code> (optional operation).
160 * Returns a negative value if this information is not available.
161 *
162 * @param key the key to query
163 * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
164 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
165 */
166 int getNumActive(K key) throws UnsupportedOperationException;
167
168 /**
169 * Returns the total number of instances
170 * currently idle in this pool (optional operation).
171 * Returns a negative value if this information is not available.
172 *
173 * @return the total number of instances currently idle in this pool or a negative value if unsupported
174 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
175 */
176 int getNumIdle() throws UnsupportedOperationException;
177
178 /**
179 * Returns the total number of instances
180 * current borrowed from this pool but not
181 * yet returned (optional operation).
182 * Returns a negative value if this information is not available.
183 *
184 * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
185 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
186 */
187 int getNumActive() throws UnsupportedOperationException;
188
189 /**
190 * Clears the pool, removing all pooled instances (optional operation).
191 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
192 *
193 * @throws UnsupportedOperationException when this implementation doesn't support the operation
194 */
195 void clear() throws Exception, UnsupportedOperationException;
196
197 /**
198 * Clears the specified pool, removing all
199 * pooled instances corresponding to
200 * the given <code>key</code> (optional operation).
201 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
202 *
203 * @param key the key to clear
204 * @throws UnsupportedOperationException when this implementation doesn't support the operation
205 */
206 void clear(K key) throws Exception, UnsupportedOperationException;
207
208 /**
209 * Close this pool, and free any resources associated with it.
210 * <p>
211 * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
212 * this method on a pool will cause them to throw an {@link IllegalStateException}.
213 * </p>
214 *
215 * @throws Exception
216 */
217 void close() throws Exception;
218
219 /**
220 * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
221 * to create new instances (optional operation).
222 * Trying to change the <code>factory</code> after a pool has been used will frequently
223 * throw an {@link UnsupportedOperationException}. It is up to the pool
224 * implementation to determine when it is acceptable to call this method.
225 *
226 * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
227 * @throws IllegalStateException when the factory cannot be set at this time
228 * @throws UnsupportedOperationException when this implementation doesn't support the operation
229 * @deprecated to be removed in pool 2.0
230 */
231 @Deprecated
232 void setFactory(KeyedPoolableObjectFactory<K, V> factory) throws IllegalStateException, UnsupportedOperationException;
233 }