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Java > Open Source Codes > org > apache > commons > logging > LogFactory


1 /*
2  * Copyright 2001-2004 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.logging;
18
19 import org.apache.commons.logging.impl.SLF4JLogFactory;
20
21 /**
22  * <p>
23  * Factory for creating {@link Log} instances, which always delegates to an instance of
24  * {@link SLF4JLogFactory}.
25  *
26  * </p>
27  *
28  * @author Craig R. McClanahan
29  * @author Costin Manolache
30  * @author Richard A. Sitze
31  * @author Ceki G&uuml;lc&uuml;
32  */

33
34 public abstract class LogFactory {
35
36   static LogFactory logFactory = new SLF4JLogFactory();
37
38   /**
39    * The name of the property used to identify the LogFactory implementation
40    * class name.
41    * <p>
42    * This property is not used but preserved here for compatibility.
43    */

44   public static final String JavaDoc FACTORY_PROPERTY =
45       "org.apache.commons.logging.LogFactory";
46
47   /**
48    * The fully qualified class name of the fallback <code>LogFactory</code>
49    * implementation class to use, if no other can be found.
50    *
51    * <p>This property is not used but preserved here for compatibility.
52    */

53   public static final String JavaDoc FACTORY_DEFAULT =
54       "org.apache.commons.logging.impl.SLF4JLogFactory";
55
56   /**
57    * The name of the properties file to search for.
58    * <p>
59    * This property is not used but preserved here for compatibility.
60    */

61   public static final String JavaDoc FACTORY_PROPERTIES =
62       "commons-logging.properties";
63
64   
65   /**
66    * Protected constructor that is not available for public use.
67    */

68   protected LogFactory() {
69   }
70
71   // --------------------------------------------------------- Public Methods
72

73   /**
74    * Return the configuration attribute with the specified name (if any), or
75    * <code>null</code> if there is no such attribute.
76    *
77    * @param name
78    * Name of the attribute to return
79    */

80   public abstract Object JavaDoc getAttribute(String JavaDoc name);
81
82   /**
83    * Return an array containing the names of all currently defined configuration
84    * attributes. If there are no such attributes, a zero length array is
85    * returned.
86    */

87   public abstract String JavaDoc[] getAttributeNames();
88
89   /**
90    * Convenience method to derive a name from the specified class and call
91    * <code>getInstance(String)</code> with it.
92    *
93    * @param clazz
94    * Class for which a suitable Log name will be derived
95    *
96    * @exception LogConfigurationException
97    * if a suitable <code>Log</code> instance cannot be returned
98    */

99   public abstract Log getInstance(Class JavaDoc clazz) throws LogConfigurationException;
100
101   /**
102    * <p>
103    * Construct (if necessary) and return a <code>Log</code> instance, using
104    * the factory's current set of configuration attributes.
105    * </p>
106    *
107    * <p>
108    * <strong>NOTE </strong>- Depending upon the implementation of the
109    * <code>LogFactory</code> you are using, the <code>Log</code> instance
110    * you are returned may or may not be local to the current application, and
111    * may or may not be returned again on a subsequent call with the same name
112    * argument.
113    * </p>
114    *
115    * @param name
116    * Logical name of the <code>Log</code> instance to be returned
117    * (the meaning of this name is only known to the underlying logging
118    * implementation that is being wrapped)
119    *
120    * @exception LogConfigurationException
121    * if a suitable <code>Log</code> instance cannot be returned
122    */

123   public abstract Log getInstance(String JavaDoc name) throws LogConfigurationException;
124
125   /**
126    * Release any internal references to previously created {@link Log}instances
127    * returned by this factory. This is useful in environments like servlet
128    * containers, which implement application reloading by throwing away a
129    * ClassLoader. Dangling references to objects in that class loader would
130    * prevent garbage collection.
131    */

132   public abstract void release();
133
134   /**
135    * Remove any configuration attribute associated with the specified name. If
136    * there is no such attribute, no action is taken.
137    *
138    * @param name
139    * Name of the attribute to remove
140    */

141   public abstract void removeAttribute(String JavaDoc name);
142
143   /**
144    * Set the configuration attribute with the specified name. Calling this with
145    * a <code>null</code> value is equivalent to calling
146    * <code>removeAttribute(name)</code>.
147    *
148    * @param name
149    * Name of the attribute to set
150    * @param value
151    * Value of the attribute to set, or <code>null</code> to remove
152    * any setting for this attribute
153    */

154   public abstract void setAttribute(String JavaDoc name, Object JavaDoc value);
155
156   // --------------------------------------------------------- Static Methods
157

158   /**
159    * <p>
160    * Construct (if necessary) and return a <code>LogFactory</code> instance,
161    * using the following ordered lookup procedure to determine the name of the
162    * implementation class to be loaded.
163    * </p>
164    * <ul>
165    * <li>The <code>org.apache.commons.logging.LogFactory</code> system
166    * property.</li>
167    * <li>The JDK 1.3 Service Discovery mechanism</li>
168    * <li>Use the properties file <code>commons-logging.properties</code>
169    * file, if found in the class path of this class. The configuration file is
170    * in standard <code>java.util.Properties</code> format and contains the
171    * fully qualified name of the implementation class with the key being the
172    * system property defined above.</li>
173    * <li>Fall back to a default implementation class (
174    * <code>org.apache.commons.logging.impl.SLF4FLogFactory</code>).</li>
175    * </ul>
176    *
177    * <p>
178    * <em>NOTE</em>- If the properties file method of identifying the
179    * <code>LogFactory</code> implementation class is utilized, all of the
180    * properties defined in this file will be set as configuration attributes on
181    * the corresponding <code>LogFactory</code> instance.
182    * </p>
183    *
184    * @exception LogConfigurationException
185    * if the implementation class is not available or cannot be
186    * instantiated.
187    */

188   public static LogFactory getFactory() throws LogConfigurationException {
189     return logFactory;
190   }
191
192   /**
193    * Convenience method to return a named logger, without the application having
194    * to care about factories.
195    *
196    * @param clazz
197    * Class from which a log name will be derived
198    *
199    * @exception LogConfigurationException
200    * if a suitable <code>Log</code> instance cannot be returned
201    */

202   public static Log getLog(Class JavaDoc clazz) throws LogConfigurationException {
203
204     return (getFactory().getInstance(clazz));
205   }
206
207   /**
208    * Convenience method to return a named logger, without the application having
209    * to care about factories.
210    *
211    * @param name
212    * Logical name of the <code>Log</code> instance to be returned
213    * (the meaning of this name is only known to the underlying logging
214    * implementation that is being wrapped)
215    *
216    * @exception LogConfigurationException
217    * if a suitable <code>Log</code> instance cannot be returned
218    */

219   public static Log getLog(String JavaDoc name) throws LogConfigurationException {
220
221     return (getFactory().getInstance(name));
222
223   }
224
225   /**
226    * Release any internal references to previously created {@link LogFactory}
227    * instances that have been associated with the specified class loader (if
228    * any), after calling the instance method <code>release()</code> on each of
229    * them.
230    *
231    * @param classLoader
232    * ClassLoader for which to release the LogFactory
233    */

234   public static void release(ClassLoader JavaDoc classLoader) {
235     // since SLF4J based JCL does not make use of classloaders, there is nothing
236
// to do here
237
}
238
239   /**
240    * Release any internal references to previously created {@link LogFactory}
241    * instances, after calling the instance method <code>release()</code> on
242    * each of them. This is useful in environments like servlet containers, which
243    * implement application reloading by throwing away a ClassLoader. Dangling
244    * references to objects in that class loader would prevent garbage
245    * collection.
246    */

247   public static void releaseAll() {
248     // since SLF4J based JCL does not make use of classloaders, there is nothing
249
// to do here
250
}
251
252 }
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