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 import java.util.NoSuchElementException;
21
22 /**
23 * A pooling interface.
24 * <p>
25 * <code>ObjectPool</code> defines a trivially simple pooling interface. The only
26 * required methods are {@link #borrowObject borrowObject}, {@link #returnObject returnObject}
27 * and {@link #invalidateObject invalidateObject}.
28 * </p>
29 * <p>
30 * Example of use:
31 * <pre style="border:solid thin; padding: 1ex;"
32 * > Object obj = <code style="color:#00C">null</code>;
33 *
34 * <code style="color:#00C">try</code> {
35 * obj = pool.borrowObject();
36 * <code style="color:#0C0">//...use the object...</code>
37 * } <code style="color:#00C">catch</code>(Exception e) {
38 * <code style="color:#0C0">// invalidate the object</code>
39 * pool.invalidateObject(obj);
40 * <code style="color:#0C0">// do not return the object to the pool twice</code>
41 * obj = <code style="color:#00C">null</code>;
42 * } <code style="color:#00C">finally</code> {
43 * <code style="color:#0C0">// make sure the object is returned to the pool</code>
44 * <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
45 * pool.returnObject(obj);
46 * }
47 * }</pre>
48 * </p>
49 *
50 * <p>See {@link BaseObjectPool} for a simple base implementation.</p>
51 *
52 * @author Rodney Waldhoff
53 * @author Sandy McArthur
54 * @version $Revision: 480413 $ $Date: 2006-11-28 22:16:05 -0700 (Tue, 28 Nov 2006) $
55 * @see PoolableObjectFactory
56 * @see ObjectPoolFactory
57 * @see KeyedObjectPool
58 * @see BaseObjectPool
59 * @since Pool 1.0
60 */
61 public interface ObjectPool {
62 /**
63 * Obtains an instance from this pool.
64 * <p>
65 * Instances returned from this method will have been either newly created with
66 * {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
67 * have been activated with {@link PoolableObjectFactory#activateObject activateObject} and
68 * then validated with {@link PoolableObjectFactory#validateObject validateObject}.
69 * </p>
70 * <p>
71 * By contract, clients <strong>must</strong> return the borrowed instance using
72 * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
73 * as defined in an implementation or sub-interface.
74 * </p>
75 * <p>
76 * The behaviour of this method when the pool has been exhausted
77 * is not strictly specified (although it may be specified by implementations).
78 * Older versions of this method would return <code>null</code> to indicate exhaustion,
79 * newer versions are encouraged to throw a {@link NoSuchElementException}.
80 * </p>
81 *
82 * @return an instance from this pool.
83 * @throws IllegalStateException after {@link #close close} has been called on this pool.
84 * @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception.
85 * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance.
86 */
87 Object borrowObject() throws Exception, NoSuchElementException, IllegalStateException;
88
89 /**
90 * Return an instance to the pool.
91 * By contract, <code>obj</code> <strong>must</strong> have been obtained
92 * using {@link #borrowObject() borrowObject}
93 * or a related method as defined in an implementation
94 * or sub-interface.
95 *
96 * @param obj a {@link #borrowObject borrowed} instance to be returned.
97 * @throws Exception <b>deprecated</b>: as of Pool 2.0 pool implementations should swallow
98 * exceptions that occur when a poolable object is returned. For future source compatability
99 * implementations of this method should not even declare that they throw any exception.
100 */
101 void returnObject(Object obj) throws Exception;
102
103 /**
104 * Invalidates an object from the pool
105 * By contract, <code>obj</code> <strong>must</strong> have been obtained
106 * using {@link #borrowObject borrowObject}
107 * or a related method as defined in an implementation
108 * or sub-interface.
109 * <p>
110 * This method should be used when an object that has been borrowed
111 * is determined (due to an exception or other problem) to be invalid.
112 * </p>
113 *
114 * @param obj a {@link #borrowObject borrowed} instance to be disposed.
115 * @throws Exception <b>deprecated</b>: as of Pool 2.0 pool implementations should swallow
116 * exceptions that occur when a poolable object is returned. For future source compatability
117 * implementations of this method should not even declare that they throw any exception.
118 */
119 void invalidateObject(Object obj) throws Exception;
120
121 /**
122 * Create an object using the {@link PoolableObjectFactory factory} or other
123 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
124 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
125 * (Optional operation).
126 *
127 * @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
128 * @throws IllegalStateException after {@link #close} has been called on this pool.
129 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
130 */
131 void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;
132
133 /**
134 * Return the number of instances
135 * currently idle in this pool (optional operation).
136 * This may be considered an approximation of the number
137 * of objects that can be {@link #borrowObject borrowed}
138 * without creating any new instances.
139 * Returns a negative value if this information is not available.
140 *
141 * @return the number of instances currently idle in this pool or a negative value if unsupported
142 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
143 */
144 int getNumIdle() throws UnsupportedOperationException;
145
146 /**
147 * Return the number of instances
148 * currently borrowed from this pool
149 * (optional operation).
150 * Returns a negative value if this information is not available.
151 *
152 * @return the number of instances currently borrowed from this pool or a negative value if unsupported
153 * @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
154 */
155 int getNumActive() throws UnsupportedOperationException;
156
157 /**
158 * Clears any objects sitting idle in the pool, releasing any
159 * associated resources (optional operation).
160 * Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
161 *
162 * @throws UnsupportedOperationException if this implementation does not support the operation
163 */
164 void clear() throws Exception, UnsupportedOperationException;
165
166 /**
167 * Close this pool, and free any resources associated with it.
168 * <p>
169 * Calling {@link #addObject} or {@link #borrowObject} after invoking
170 * this method on a pool will cause them to throw an
171 * {@link IllegalStateException}.
172 * </p>
173 *
174 * @throws Exception <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
175 */
176 void close() throws Exception;
177
178 /**
179 * Sets the {@link PoolableObjectFactory factory} this pool uses
180 * to create new instances (optional operation). Trying to change
181 * the <code>factory</code> after a pool has been used will frequently
182 * throw an {@link UnsupportedOperationException}. It is up to the pool
183 * implementation to determine when it is acceptable to call this method.
184 *
185 * @param factory the {@link PoolableObjectFactory} used to create new instances.
186 * @throws IllegalStateException when the factory cannot be set at this time
187 * @throws UnsupportedOperationException if this implementation does not support the operation
188 */
189 void setFactory(PoolableObjectFactory factory) throws IllegalStateException, UnsupportedOperationException;
190 }
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