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Java > Open Source Codes > listeners > ContextListener


1 /*
2 * Copyright 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 listeners;
18
19
20 import javax.servlet.ServletContext JavaDoc;
21 import javax.servlet.ServletContextAttributeEvent JavaDoc;
22 import javax.servlet.ServletContextAttributeListener JavaDoc;
23 import javax.servlet.ServletContextEvent JavaDoc;
24 import javax.servlet.ServletContextListener JavaDoc;
25
26
27 /**
28  * Example listener for context-related application events, which were
29  * introduced in the 2.3 version of the Servlet API. This listener
30  * merely documents the occurrence of such events in the application log
31  * associated with our servlet context.
32  *
33  * @author Craig R. McClanahan
34  * @version $Revision: 1.3 $ $Date: 2006/10/12 14:31:30 $
35  */
36
37 public final class ContextListener
38     implements ServletContextAttributeListener JavaDoc, ServletContextListener JavaDoc {
39
40
41     // ----------------------------------------------------- Instance Variables
42
43
44     /**
45      * The servlet context with which we are associated.
46      */
47     private ServletContext JavaDoc context = null;
48
49
50     // --------------------------------------------------------- Public Methods
51
52
53     /**
54      * Record the fact that a servlet context attribute was added.
55      *
56      * @param event The servlet context attribute event
57      */
58     public void attributeAdded(ServletContextAttributeEvent JavaDoc event) {
59
60     log("attributeAdded('" + event.getName() + "', '" +
61         event.getValue() + "')");
62
63     }
64
65
66     /**
67      * Record the fact that a servlet context attribute was removed.
68      *
69      * @param event The servlet context attribute event
70      */
71     public void attributeRemoved(ServletContextAttributeEvent JavaDoc event) {
72
73     log("attributeRemoved('" + event.getName() + "', '" +
74         event.getValue() + "')");
75
76     }
77
78
79     /**
80      * Record the fact that a servlet context attribute was replaced.
81      *
82      * @param event The servlet context attribute event
83      */
84     public void attributeReplaced(ServletContextAttributeEvent JavaDoc event) {
85
86     log("attributeReplaced('" + event.getName() + "', '" +
87         event.getValue() + "')");
88
89     }
90
91
92     /**
93      * Record the fact that this web application has been destroyed.
94      *
95      * @param event The servlet context event
96      */
97     public void contextDestroyed(ServletContextEvent JavaDoc event) {
98
99     log("contextDestroyed()");
100     this.context = null;
101
102     }
103
104
105     /**
106      * Record the fact that this web application has been initialized.
107      *
108      * @param event The servlet context event
109      */
110     public void contextInitialized(ServletContextEvent JavaDoc event) {
111
112     this.context = event.getServletContext();
113     log("contextInitialized()");
114
115     }
116
117
118     // -------------------------------------------------------- Private Methods
119
120
121     /**
122      * Log a message to the servlet context application log.
123      *
124      * @param message Message to be logged
125      */
126     private void log(String JavaDoc message) {
127
128     if (context != null)
129         context.log("ContextListener: " + message);
130     else
131         System.out.println("ContextListener: " + message);
132
133     }
134
135
136     /**
137      * Log a message and associated exception to the servlet context
138      * application log.
139      *
140      * @param message Message to be logged
141      * @param throwable Exception to be logged
142      */
143     private void log(String JavaDoc message, Throwable JavaDoc throwable) {
144
145     if (context != null)
146         context.log("ContextListener: " + message, throwable);
147     else {
148         System.out.println("ContextListener: " + message);
149         throwable.printStackTrace(System.out);
150     }
151
152     }
153
154
155 }
156
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