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    }