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18 package org.apache.commons.pool;
19
20 /***
21 * An interface defining life-cycle methods for
22 * instances to be served by a {@link KeyedObjectPool}.
23 * <p>
24 * By contract, when an {@link KeyedObjectPool}
25 * delegates to a {@link KeyedPoolableObjectFactory},
26 * <ol>
27 * <li>
28 * {@link #makeObject makeObject}
29 * is called whenever a new instance is needed.
30 * </li>
31 * <li>
32 * {@link #activateObject activateObject}
33 * is invoked on every instance that has been
34 * {@link #passivateObject passivated} before it is
35 * {@link KeyedObjectPool#borrowObject borrowed} from the pool.
36 * </li>
37 * <li>
38 * {@link #validateObject validateObject}
39 * is invoked on {@link #activateObject activated} instances to make sure
40 * they can be {@link KeyedObjectPool#borrowObject borrowed} from the pool.
41 * <code>validateObject</code> <strong>may</strong> also be used to test an
42 * instance being {@link KeyedObjectPool#returnObject returned} to the pool
43 * before it is {@link #passivateObject passivated}. It will only be invoked
44 * on an activated instance.
45 * </li>
46 * <li>
47 * {@link #passivateObject passivateObject}
48 * is invoked on every instance when it is returned to the pool.
49 * </li>
50 * <li>
51 * {@link #destroyObject destroyObject}
52 * is invoked on every instance when it is being "dropped" from the
53 * pool (whether due to the response from <code>validateObject</code>,
54 * or for reasons specific to the pool implementation.) There is no
55 * guarantee that the instance being destroyed will
56 * be considered active, passive or in a generally consistent state.
57 * </li>
58 * </ol>
59 * </p>
60 * <p>
61 * {@link KeyedPoolableObjectFactory} must be thread-safe. The only promise
62 * an {@link KeyedObjectPool} makes is that the same instance of an object will not
63 * be passed to more than one method of a <code>KeyedPoolableObjectFactory</code>
64 * at a time.
65 * </p>
66 *
67 * @see KeyedObjectPool
68 *
69 * @author Rodney Waldhoff
70 * @author Sandy McArthur
71 * @version $Revision: 480413 $ $Date: 2006-11-28 22:16:05 -0700 (Tue, 28 Nov 2006) $
72 * @since Pool 1.0
73 */
74 public interface KeyedPoolableObjectFactory {
75 /***
76 * Create an instance that can be served by the pool.
77 * Instances returned from this method should be in the
78 * same state as if they had been
79 * {@link #activateObject activated}. They will not be
80 * activated before being served by the pool.
81 *
82 * @param key the key used when constructing the object
83 * @return an instance that can be served by the pool.
84 * @throws Exception if there is a problem creating a new instance,
85 * this will be propagated to the code requesting an object.
86 */
87 Object makeObject(Object key) throws Exception;
88
89 /***
90 * Destroy an instance no longer needed by the pool.
91 * <p>
92 * It is important for implementations of this method to be aware
93 * that there is no guarantee about what state <code>obj</code>
94 * will be in and the implementation should be prepared to handle
95 * unexpected errors.
96 * </p>
97 * <p>
98 * Also, an implementation must take in to consideration that
99 * instances lost to the garbage collector may never be destroyed.
100 * </p>
101 *
102 * @param key the key used when selecting the instance
103 * @param obj the instance to be destroyed
104 * @throws Exception should be avoided as it may be swallowed by
105 * the pool implementation.
106 * @see #validateObject
107 * @see KeyedObjectPool#invalidateObject
108 */
109 void destroyObject(Object key, Object obj) throws Exception;
110
111 /***
112 * Ensures that the instance is safe to be returned by the pool.
113 * Returns <code>false</code> if <code>obj</code> should be destroyed.
114 *
115 * @param key the key used when selecting the object
116 * @param obj the instance to be validated
117 * @return <code>false</code> if <code>obj</code> is not valid and should
118 * be dropped from the pool, <code>true</code> otherwise.
119 */
120 boolean validateObject(Object key, Object obj);
121
122 /***
123 * Reinitialize an instance to be returned by the pool.
124 *
125 * @param key the key used when selecting the object
126 * @param obj the instance to be activated
127 * @throws Exception if there is a problem activating <code>obj</code>,
128 * this exception may be swallowed by the pool.
129 * @see #destroyObject
130 */
131 void activateObject(Object key, Object obj) throws Exception;
132
133 /***
134 * Uninitialize an instance to be returned to the idle object pool.
135 *
136 * @param key the key used when selecting the object
137 * @param obj the instance to be passivated
138 * @throws Exception if there is a problem passivating <code>obj</code>,
139 * this exception may be swallowed by the pool.
140 * @see #destroyObject
141 */
142 void passivateObject(Object key, Object obj) throws Exception;
143 }