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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: 480413 $ $Date: 2006-11-28 22:16:05 -0700 (Tue, 28 Nov 2006) $
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 <b>deprecated</b>: as of Pool 2.0 pool implementations should swallow
107 * exceptions that occur when a poolable object is returned. For future source compatability
108 * implementations of this method should not even declare that they throw any exception.
109 */
110 void returnObject(Object key, Object obj) throws Exception;
111
112 /***
113 * Invalidates an object from the pool
114 * By contract, <code>obj</code> <strong>must</strong> have been obtained
115 * using {@link #borrowObject borrowObject}
116 * or a related method as defined in an implementation
117 * or sub-interface
118 * using a <code>key</code> that is equivalent to the one used to
119 * borrow the <code>Object</code> in the first place.
120 * <p>
121 * 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.
123 * </p>
124 *
125 * @param key the key used to obtain the object
126 * @param obj a {@link #borrowObject borrowed} instance to be returned.
127 * @throws Exception <b>deprecated</b>: as of Pool 2.0 pool implementations should swallow
128 * exceptions that occur when a poolable object is returned. For future source compatability
129 * implementations of this method should not even declare that they throw any exception.
130 */
131 void invalidateObject(Object key, Object obj) throws Exception;
132
133 /***
134 * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
135 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
136 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
137 * (Optional operation).
138 *
139 * @param key the key a new instance should be added to
140 * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
141 * @throws IllegalStateException after {@link #close} has been called on this pool.
142 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
143 */
144 void addObject(Object key) throws Exception, IllegalStateException, UnsupportedOperationException;
145
146 /***
147 * Returns the number of instances
148 * corresponding to the given <code>key</code>
149 * currently idle in this pool (optional operation).
150 * Returns a negative value if this information is not available.
151 *
152 * @param key the key to query
153 * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
154 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
155 */
156 int getNumIdle(Object key) throws UnsupportedOperationException;
157
158 /***
159 * Returns the number of instances
160 * currently borrowed from but not yet returned
161 * to the pool corresponding to the
162 * given <code>key</code> (optional operation).
163 * Returns a negative value if this information is not available.
164 *
165 * @param key the key to query
166 * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
167 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
168 */
169 int getNumActive(Object key) throws UnsupportedOperationException;
170
171 /***
172 * Returns the total number of instances
173 * currently idle in this pool (optional operation).
174 * Returns a negative value if this information is not available.
175 *
176 * @return the total number of instances currently idle in this pool or a negative value if unsupported
177 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
178 */
179 int getNumIdle() throws UnsupportedOperationException;
180
181 /***
182 * Returns the total number of instances
183 * current borrowed from this pool but not
184 * yet returned (optional operation).
185 * Returns a negative value if this information is not available.
186 *
187 * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
188 * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
189 */
190 int getNumActive() throws UnsupportedOperationException;
191
192 /***
193 * Clears the pool, removing all pooled instances (optional operation).
194 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
195 *
196 * @throws UnsupportedOperationException when this implementation doesn't support the operation
197 */
198 void clear() throws Exception, UnsupportedOperationException;
199
200 /***
201 * Clears the specified pool, removing all
202 * pooled instances corresponding to
203 * the given <code>key</code> (optional operation).
204 * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
205 *
206 * @param key the key to clear
207 * @throws UnsupportedOperationException when this implementation doesn't support the operation
208 */
209 void clear(Object key) throws Exception, UnsupportedOperationException;
210
211 /***
212 * Close this pool, and free any resources associated with it.
213 * <p>
214 * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
215 * this method on a pool will cause them to throw an {@link IllegalStateException}.
216 * </p>
217 *
218 * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
219 */
220 void close() throws Exception;
221
222 /***
223 * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
224 * to create new instances (optional operation).
225 * Trying to change the <code>factory</code> after a pool has been used will frequently
226 * throw an {@link UnsupportedOperationException}. It is up to the pool
227 * implementation to determine when it is acceptable to call this method.
228 *
229 * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
230 * @throws IllegalStateException when the factory cannot be set at this time
231 * @throws UnsupportedOperationException when this implementation doesn't support the operation
232 */
233 void setFactory(KeyedPoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
234 }