View Javadoc

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: 155430 $ $Date: 2005-02-26 08:13:28 -0500 (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 borrowObject() throws Exception;
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 obj) throws Exception;
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 obj) throws Exception;
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;
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;
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;
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, UnsupportedOperationException;
127 
128     /***
129      * Close this pool, and free any resources associated with it.
130      */
131     void close() throws Exception;
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, UnsupportedOperationException;
142 }