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: 962893 $ $Date: 2010-07-10 10:37:27 -0700 (Sat, 10 Jul 2010) $
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 * <p>Invalidates an object from the pool.</p>
112 *
113 * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
114 * using {@link #borrowObject borrowObject} or a related method as defined
115 * in an implementation or sub-interface using a <code>key</code> that is
116 * equivalent to the one used to borrow the <code>Object</code> in the first place.</p>
117 *
118 * <p>This method should be used when an object that has been borrowed
119 * is determined (due to an exception or other problem) to be invalid.</p>
120 *
121 * @param key the key used to obtain the object
122 * @param obj a {@link #borrowObject borrowed} instance to be returned.
123 * @throws Exception
124 */
125 void invalidateObject(Object key, Object obj) throws Exception;
126
127 /**
128 * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
129 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
130 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
131 * (Optional operation).
132 *
133 * @param key the key a new instance should be added to
134 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
135 * @throws IllegalStateException after {@link #close} has been called on this pool.
136 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
137 */
138 void addObject(Object key) throws Exception, IllegalStateException, UnsupportedOperationException;
139
140 /**
141 * Returns the number of instances
142 * corresponding to the given <code>key</code>
143 * currently idle in this pool (optional operation).
144 * Returns a negative value if this information is not available.
145 *
146 * @param key the key to query
147 * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
148 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
149 */
150 int getNumIdle(Object key) throws UnsupportedOperationException;
151
152 /**
153 * Returns the number of instances
154 * currently borrowed from but not yet returned
155 * to the pool corresponding to the
156 * given <code>key</code> (optional operation).
157 * Returns a negative value if this information is not available.
158 *
159 * @param key the key to query
160 * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
161 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
162 */
163 int getNumActive(Object key) throws UnsupportedOperationException;
164
165 /**
166 * Returns the total number of instances
167 * currently idle in this pool (optional operation).
168 * Returns a negative value if this information is not available.
169 *
170 * @return the total number of instances currently idle in this pool or a negative value if unsupported
171 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
172 */
173 int getNumIdle() throws UnsupportedOperationException;
174
175 /**
176 * Returns the total number of instances
177 * current borrowed from this pool but not
178 * yet returned (optional operation).
179 * Returns a negative value if this information is not available.
180 *
181 * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
182 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
183 */
184 int getNumActive() throws UnsupportedOperationException;
185
186 /**
187 * Clears the pool, removing all pooled instances (optional operation).
188 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
189 *
190 * @throws UnsupportedOperationException when this implementation doesn't support the operation
191 */
192 void clear() throws Exception, UnsupportedOperationException;
193
194 /**
195 * Clears the specified pool, removing all
196 * pooled instances corresponding to
197 * the given <code>key</code> (optional operation).
198 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
199 *
200 * @param key the key to clear
201 * @throws UnsupportedOperationException when this implementation doesn't support the operation
202 */
203 void clear(Object key) throws Exception, UnsupportedOperationException;
204
205 /**
206 * Close this pool, and free any resources associated with it.
207 * <p>
208 * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
209 * this method on a pool will cause them to throw an {@link IllegalStateException}.
210 * </p>
211 *
212 * @throws Exception
213 */
214 void close() throws Exception;
215
216 /**
217 * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
218 * to create new instances (optional operation).
219 * Trying to change the <code>factory</code> after a pool has been used will frequently
220 * throw an {@link UnsupportedOperationException}. It is up to the pool
221 * implementation to determine when it is acceptable to call this method.
222 *
223 * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
224 * @throws IllegalStateException when the factory cannot be set at this time
225 * @throws UnsupportedOperationException when this implementation doesn't support the operation
226 * @deprecated to be removed in pool 2.0
227 */
228 void setFactory(KeyedPoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
229 }