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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.pool;
19  
20  import java.util.NoSuchElementException;
21  
22  /**
23   * A "keyed" pooling interface.
24   * <p>
25   * A keyed pool pools instances of multiple types. Each
26   * type may be accessed using an arbitrary key.
27   * </p>
28   * <p>
29   * Example of use:
30   * <pre style="border:solid thin; padding: 1ex;"
31   * > Object obj = <code style="color:#00C">null</code>;
32   * Object key = <code style="color:#C00">"Key"</code>;
33   *
34   * <code style="color:#00C">try</code> {
35   *     obj = pool.borrowObject(key);
36   *     <code style="color:#0C0">//...use the object...</code>
37   * } <code style="color:#00C">catch</code>(Exception e) {
38   *     <code style="color:#0C0">// invalidate the object</code>
39   *     pool.invalidateObject(key, obj);
40   *     <code style="color:#0C0">// do not return the object to the pool twice</code>
41   *     obj = <code style="color:#00C">null</code>;
42   * } <code style="color:#00C">finally</code> {
43   *     <code style="color:#0C0">// make sure the object is returned to the pool</code>
44   *     <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
45   *         pool.returnObject(key, obj);
46   *     }
47   * }</pre>
48   * </p>
49   * <p>
50   * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most
51   * one instance per key value, or may choose to maintain a pool of instances
52   * for each key (essentially creating a {@link java.util.Map Map} of
53   * {@link ObjectPool pools}).
54   * </p>
55   *
56   * <p>See {@link BaseKeyedObjectPool} for a simple base implementation.</p>
57   *
58   * @author Rodney Waldhoff
59   * @author Sandy McArthur
60   * @version $Revision: 778480 $ $Date: 2009-05-25 15:34:55 -0400 (Mon, 25 May 2009) $
61   * @see KeyedPoolableObjectFactory
62   * @see KeyedObjectPoolFactory
63   * @see ObjectPool
64   * @see BaseKeyedObjectPool
65   * @since Pool 1.0
66   */
67  public interface KeyedObjectPool {
68      /**
69       * Obtains an instance from this pool for the specified <code>key</code>.
70       * <p>
71       * Instances returned from this method will have been either newly created with
72       * {@link KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
73       * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and
74       * then validated with {@link KeyedPoolableObjectFactory#validateObject validateObject}.
75       * <p>
76       * By contract, clients <strong>must</strong> return the borrowed object using
77       * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
78       * as defined in an implementation or sub-interface,
79       * using a <code>key</code> that is {@link Object#equals equivalent} to the one used to
80       * borrow the instance in the first place.
81       * <p>
82       * The behaviour of this method when the pool has been exhausted
83       * is not strictly specified (although it may be specified by implementations).
84       * Older versions of this method would return <code>null</code> to indicate exhaustion,
85       * newer versions are encouraged to throw a {@link NoSuchElementException}.
86       *
87       * @param key the key used to obtain the object
88       * @return an instance from this pool.
89       * @throws IllegalStateException after {@link #close close} has been called on this pool
90       * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject makeObject} throws an exception
91       * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance
92       */
93      Object borrowObject(Object key) throws Exception, NoSuchElementException, IllegalStateException;
94  
95      /**
96       * Return an instance to the pool.
97       * By contract, <code>obj</code> <strong>must</strong> have been obtained
98       * using {@link #borrowObject borrowObject}
99       * 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 }