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 /**
21 * An interface defining life-cycle methods for
22 * instances to be served by an {@link ObjectPool}.
23 * <p>
24 * By contract, when an {@link ObjectPool}
25 * delegates to a {@link PoolableObjectFactory},
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 ObjectPool#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 ObjectPool#borrowObject borrowed} from the pool.
41 * <code>validateObject</code> <strong>may</strong> also be used to test an
42 * instance being {@link ObjectPool#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 PoolableObjectFactory} must be thread-safe. The only promise
62 * an {@link ObjectPool} makes is that the same instance of an object will not
63 * be passed to more than one method of a <code>PoolableObjectFactory</code>
64 * at a time.
65 * </p>
66 *
67 * @see ObjectPool
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 PoolableObjectFactory {
75 /**
76 * Creates 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 * @return an instance that can be served by the pool.
83 * @throws Exception if there is a problem creating a new instance,
84 * this will be propagated to the code requesting an object.
85 */
86 Object makeObject() throws Exception;
87
88 /**
89 * Destroys an instance no longer needed by the pool.
90 * <p>
91 * It is important for implementations of this method to be aware
92 * that there is no guarantee about what state <code>obj</code>
93 * will be in and the implementation should be prepared to handle
94 * unexpected errors.
95 * </p>
96 * <p>
97 * Also, an implementation must take in to consideration that
98 * instances lost to the garbage collector may never be destroyed.
99 * </p>
100 *
101 * @param obj the instance to be destroyed
102 * @throws Exception should be avoided as it may be swallowed by
103 * the pool implementation.
104 * @see #validateObject
105 * @see ObjectPool#invalidateObject
106 */
107 void destroyObject(Object obj) throws Exception;
108
109 /**
110 * Ensures that the instance is safe to be returned by the pool.
111 * Returns <code>false</code> if <code>obj</code> should be destroyed.
112 *
113 * @param obj the instance to be validated
114 * @return <code>false</code> if <code>obj</code> is not valid and should
115 * be dropped from the pool, <code>true</code> otherwise.
116 */
117 boolean validateObject(Object obj);
118
119 /**
120 * Reinitialize an instance to be returned by the pool.
121 *
122 * @param obj the instance to be activated
123 * @throws Exception if there is a problem activating <code>obj</code>,
124 * this exception may be swallowed by the pool.
125 * @see #destroyObject
126 */
127 void activateObject(Object obj) throws Exception;
128
129 /**
130 * Uninitialize an instance to be returned to the idle object pool.
131 *
132 * @param obj the instance to be passivated
133 * @throws Exception if there is a problem passivating <code>obj</code>,
134 * this exception may be swallowed by the pool.
135 * @see #destroyObject
136 */
137 void passivateObject(Object obj) throws Exception;
138 }
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