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Java > Open Source Codes > org > apache > commons > pool > ObjectPool


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16
17 package org.apache.commons.pool;
18
19 /**
20  * A pooling interface.
21  * <p>
22  * <code>ObjectPool</code> defines a trivially simple pooling interface. The only
23  * required methods are {@link #borrowObject borrowObject} and {@link #returnObject returnObject}.
24  * <p>
25  * Example of use:
26  * <table border="1" cellspacing="0" cellpadding="3" align="center" bgcolor="#FFFFFF"><tr><td><pre>
27  * Object obj = <font color="#0000CC">null</font>;
28  *
29  * <font color="#0000CC">try</font> {
30  * obj = pool.borrowObject();
31  * <font color="#00CC00">//...use the object...</font>
32  * } <font color="#0000CC">catch</font>(Exception e) {
33  * <font color="#00CC00">//...handle any exceptions...</font>
34  * } <font color="#0000CC">finally</font> {
35  * <font color="#00CC00">// make sure the object is returned to the pool</font>
36  * <font color="#0000CC">if</font>(<font color="#0000CC">null</font> != obj) {
37  * pool.returnObject(obj);
38  * }
39  * }</pre></td></tr></table>
40  * See {@link org.apache.commons.pool.BaseObjectPool BaseObjectPool} for a simple base implementation.
41  *
42  * @author Rodney Waldhoff
43  * @version $Revision$ $Date: 2005-02-26 05:13:28 -0800 (Sat, 26 Feb 2005) $
44  *
45  */
46 public interface ObjectPool {
47     /**
48      * Obtain an instance from my pool.
49      * By contract, clients MUST return
50      * the borrowed instance using
51      * {@link #returnObject(java.lang.Object) returnObject}
52      * or a related method as defined in an implementation
53      * or sub-interface.
54      * <p>
55      * The behaviour of this method when the pool has been exhausted
56      * is not specified (although it may be specified by implementations).
57      *
58      * @return an instance from my pool.
59      */
60     Object JavaDoc borrowObject() throws Exception JavaDoc;
61
62     /**
63      * Return an instance to my pool.
64      * By contract, <i>obj</i> MUST have been obtained
65      * using {@link #borrowObject() borrowObject}
66      * or a related method as defined in an implementation
67      * or sub-interface.
68      *
69      * @param obj a {@link #borrowObject borrowed} instance to be returned.
70      */
71     void returnObject(Object JavaDoc obj) throws Exception JavaDoc;
72
73     /**
74      * Invalidates an object from the pool
75      * By contract, <i>obj</i> MUST have been obtained
76      * using {@link #borrowObject() borrowObject}
77      * or a related method as defined in an implementation
78      * or sub-interface.
79      * <p>
80      * This method should be used when an object that has been borrowed
81      * is determined (due to an exception or other problem) to be invalid.
82      * If the connection should be validated before or after borrowing,
83      * then the {@link PoolableObjectFactory#validateObject} method should be
84      * used instead.
85      *
86      * @param obj a {@link #borrowObject borrowed} instance to be returned.
87      */
88     void invalidateObject(Object JavaDoc obj) throws Exception JavaDoc;
89
90     /**
91      * Create an object using my {@link #setFactory factory} or other
92      * implementation dependent mechanism, and place it into the pool.
93      * addObject() is useful for "pre-loading" a pool with idle objects.
94      * (Optional operation).
95      */
96     void addObject() throws Exception JavaDoc;
97
98     /**
99      * Return the number of instances
100      * currently idle in my pool (optional operation).
101      * This may be considered an approximation of the number
102      * of objects that can be {@link #borrowObject borrowed}
103      * without creating any new instances.
104      *
105      * @return the number of instances currently idle in my pool
106      * @throws UnsupportedOperationException if this implementation does not support the operation
107      */
108     int getNumIdle() throws UnsupportedOperationException JavaDoc;
109
110     /**
111      * Return the number of instances
112      * currently borrowed from my pool
113      * (optional operation).
114      *
115      * @return the number of instances currently borrowed in my pool
116      * @throws UnsupportedOperationException if this implementation does not support the operation
117      */
118     int getNumActive() throws UnsupportedOperationException JavaDoc;
119
120     /**
121      * Clears any objects sitting idle in the pool, releasing any
122      * associated resources (optional operation).
123      *
124      * @throws UnsupportedOperationException if this implementation does not support the operation
125      */
126     void clear() throws Exception JavaDoc, UnsupportedOperationException JavaDoc;
127
128     /**
129      * Close this pool, and free any resources associated with it.
130      */
131     void close() throws Exception JavaDoc;
132
133     /**
134      * Sets the {@link PoolableObjectFactory factory} I use
135      * to create new instances (optional operation).
136      * @param factory the {@link PoolableObjectFactory} I use to create new instances.
137      *
138      * @throws IllegalStateException when the factory cannot be set at this time
139      * @throws UnsupportedOperationException if this implementation does not support the operation
140      */
141     void setFactory(PoolableObjectFactory factory) throws IllegalStateException JavaDoc, UnsupportedOperationException JavaDoc;
142 }
143
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