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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   * A simple base implementation of {@link ObjectPool}.
22   * Optional operations are implemented to either do nothing, return a value
23   * indicating it is unsupported or throw {@link UnsupportedOperationException}.
24   *
25   * @author Rodney Waldhoff
26   * @author Sandy McArthur
27   * @version $Revision: 791364 $ $Date: 2009-07-05 21:52:27 -0400 (Sun, 05 Jul 2009) $
28   * @since Pool 1.0
29   */
30  public abstract class BaseObjectPool implements ObjectPool {
31      /**
32       * Obtains an instance from the pool.
33       * 
34       * @return an instance from the pool
35       * @throws Exception if an instance cannot be obtained from the pool
36       */
37      public abstract Object borrowObject() throws Exception;
38      
39      /**
40       * Returns an instance to the pool.
41       * 
42       * @param obj instance to return to the pool
43       */
44      public abstract void returnObject(Object obj) throws Exception;
45      
46      /**
47       * Invalidates an object from the pool.
48       * By contract, <code>obj</code> <strong>must</strong> have been obtained
49       * using {@link #borrowObject borrowObject}
50       * or a related method as defined in an implementation
51       * or sub-interface.
52       * <p>
53       * This method should be used when an object that has been borrowed
54       * is determined (due to an exception or other problem) to be invalid.
55       * </p>
56       *
57       * @param obj a {@link #borrowObject borrowed} instance to be disposed.
58       * @throws Exception 
59       */
60      public abstract void invalidateObject(Object obj) throws Exception;
61  
62      /**
63       * Not supported in this base implementation.
64       * @return a negative value.
65       * 
66       * @throws UnsupportedOperationException
67       */
68      public int getNumIdle() throws UnsupportedOperationException {
69          return -1;
70      }
71  
72      /**
73       * Not supported in this base implementation.
74       * @return a negative value.
75       * 
76       * @throws UnsupportedOperationException
77       */
78      public int getNumActive() throws UnsupportedOperationException {
79          return -1;
80      }
81  
82      /**
83       * Not supported in this base implementation.
84       * 
85       * @throws UnsupportedOperationException
86       */
87      public void clear() throws Exception, UnsupportedOperationException {
88          throw new UnsupportedOperationException();
89      }
90  
91      /**
92       * Not supported in this base implementation.
93       * Always throws an {@link UnsupportedOperationException},
94       * subclasses should override this behavior.
95       * 
96       * @throws UnsupportedOperationException
97       */
98      public void addObject() throws Exception, UnsupportedOperationException {
99          throw new UnsupportedOperationException();
100     }
101 
102     /**
103      * Close this pool.
104      * This affects the behavior of <code>isClosed</code> and <code>assertOpen</code>.
105      */
106     public void close() throws Exception {
107         closed = true;
108     }
109 
110     /**
111      * Not supported in this base implementation.
112      * Always throws an {@link UnsupportedOperationException},
113      * subclasses should override this behavior.
114      * 
115      * @param factory the PoolableObjectFactory
116      * @throws UnsupportedOperationException
117      * @throws IllegalStateException
118      */
119     public void setFactory(PoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException {
120         throw new UnsupportedOperationException();
121     }
122 
123     /**
124      * Has this pool instance been closed.
125      * @return <code>true</code> when this pool has been closed.
126      */
127     protected final boolean isClosed() {
128         return closed;
129     }
130 
131     /**
132      * Throws an <code>IllegalStateException</code> when this pool has been closed.
133      * @throws IllegalStateException when this pool has been closed.
134      * @see #isClosed()
135      */
136     protected final void assertOpen() throws IllegalStateException {
137         if (isClosed()) {
138             throw new IllegalStateException("Pool not open");
139         }
140     }
141 
142     /** Whether or not the pool is closed */
143     private volatile boolean closed = false;
144 }