ConfigurationManager


1   package com.teamkonzept.lib;
2   
3   import java.util.Hashtable  ;
4   import java.util.Vector  ;
5   
6   /**
7    * The Configuration Manager is designed as a registry for Configuration
8    * Listeners. These listeners may register themselves in different arbitrary
9    * contexts. Notification of registered listeners is triggered by a dedicated
10   * method.
11   *
12   * @version 1.0
13   * @since 1.0
14   * @author &copy; 2001 Team-Konzept
15   */
16  public class ConfigurationManager
17  {
18  
19      // $Header: /cvsroot/webman-cms/source/webman/com/teamkonzept/lib/ConfigurationManager.java,v 1.3 2001/02/14 15:07:11 uli Exp $
20  
21      // Constants
22  
23      /**
24       * The singleton instance of the Configuration Manager.
25       */
26      private static ConfigurationManager SINGLETON = null;
27  
28  
29      // Attributes
30  
31      /**
32       * The registry for the listeners.
33       */
34      private Hashtable   registry = null;
35  
36  
37      // Constructors
38  
39      /**
40       * Avoids external instantiation.
41       */
42      private ConfigurationManager ()
43      {
44          this.registry = new Hashtable  ();
45      }
46  
47  
48      // Singleton access
49  
50      /**
51       * Returns the singleton instance of the Configuration Manager.
52       *
53       * @return the singleton instance of the Configuration Manager.
54       */
55      public static synchronized ConfigurationManager getInstance ()
56      {
57          if (SINGLETON == null)
58          {
59              SINGLETON = new ConfigurationManager();
60          }
61  
62          return SINGLETON;
63      }
64  
65  
66      // Method implementations
67  
68      /**
69       * Registers a configuration listener with the manager.
70       * <P>
71       * The method silently returns when either the listener or the
72       * context object is null.
73       *
74       * @param listener a configuration listener.
75       * @param context a registration context.
76       */
77      public synchronized void registerConfigurationListener (ConfigurationListener listener,
78                                                              Object   context)
79      {
80          if (listener == null ||
81              context == null)
82          {
83              // Fail fast and safe ;-)
84              return;
85          }
86  
87          // Read registry.
88          Vector   registrees = (Vector  ) registry.get(context);
89  
90          if (registrees == null)
91          {
92              // Create listeners container.
93              registrees = new Vector  ();
94          }
95  
96          // Add registree.
97          registrees.addElement(listener);
98  
99          // Update registry.
100         registry.put(context, registrees);
101     }
102 
103     /**
104      * Deregisters a configuration listener with the manager.
105      * <P>
106      * The method silently returns when either the listener or the
107      * context object is null.
108      *
109      * @param listener a configuration listener.
110      * @param context a registration context.
111      */
112     public synchronized void deregisterConfigurationListener (ConfigurationListener listener,
113                                                               Object   context)
114     {
115         if (listener == null ||
116             context == null)
117         {
118             // Fail fast and safe ;-)
119             return;
120         }
121 
122         // Read registry.
123         Vector   registrees = (Vector  ) registry.get(context);
124 
125         if (registrees == null)
126         {
127             // Terminate.
128             return;
129         }
130 
131         // Remove registree.
132         registrees.removeElement(listener);
133 
134         // Update registry.
135         if (registrees.size() > 0)
136         {
137             registry.put(context, registrees);
138         }
139         else
140         {
141             registry.remove(context);
142         }
143     }
144 
145     /**
146      * Notifies all listeners filed under the registration context.
147      * <P>
148      * The method silently returns when the context object is null.
149      *
150      * @param context a registration context.
151      */
152     public synchronized void notifyListeners (Object   context)
153         throws TKException
154     {
155         if (context == null)
156         {
157             // Fail fast and safe ;-)
158             return;
159         }
160 
161         // Read registry.
162         Vector   registrees = (Vector  ) registry.get(context);
163 
164         if (registrees == null)
165         {
166             // Terminate.
167             return;
168         }
169 
170         // Use index driven iteration instead of an enumeration
171         // to avoid short lived object creation.
172         for (int i = 0; i < registrees.size(); i++)
173         {
174             // Notify listener.
175             ((ConfigurationListener) registrees.elementAt(i)).configurationChanged();
176         }
177     }
178 
179 }
180
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