ActionFlowConfigRegistry


1   /*
2    * Copyright (c) 2003, Inversoft
3    *
4    * This software is distribuable under the GNU Lesser General Public License.
5    * For more information visit gnu.org.
6    */
7   package com.inversoft.verge.mvc.controller.actionflow.config;
8   
9   
10  import java.util.HashMap  ;
11  import java.util.Iterator  ;
12  import java.util.Map  ;
13  
14  import javax.servlet.ServletRequest  ;
15  
16  import com.inversoft.config.ConfigRegistry;
17  import com.inversoft.util.StringTools;
18  
19  
20  /**
21   * This class stores all the configuration objects models. This 
22   * includes the top level Namespace objects which in 
23   * turn contain the Node and ActionLink objects.
24   *
25   * @author  Brian Pontarelli
26   * @since   2.0
27   * @version 2.0
28   */
29  public class ActionFlowConfigRegistry implements ConfigRegistry {
30  
31      /**
32       * The key that the registry is stored under in the request to ensure that
33       * for a single request to the server, the configuration remains the same
34       */
35      public static final String   KEY = ActionFlowConfigRegistry.class.getName();
36  
37      /**
38       * ThreadLocals will NOT work because containers use Thread pooling so the
39       * execute Thread probably has already been used and the ThreadLocal will 
40       * already have been setup
41       */
42      private static volatile ActionFlowConfigRegistry instance =
43          new ActionFlowConfigRegistry();
44  
45  
46      /**
47       * The Map used to store all the Namespaces
48       */
49      private Map   namespaces;
50  
51  
52      /**
53       * Singleton class
54       */
55      protected ActionFlowConfigRegistry() {
56          namespaces = new HashMap  ();
57      }
58  
59      /**
60       * Creates a new instance identical to the given instance
61       */
62      ActionFlowConfigRegistry(ActionFlowConfigRegistry orig) {
63          namespaces = new HashMap  ();
64          namespaces.putAll(orig.namespaces);
65      }
66  
67  
68      /**
69       * <p>
70       * Singleton accessor method except that the HttpServletRequest is used in 
71       * order to maintain the context of a single request. Since a single request
72       * could be in progress while the configuration is changing, this prevents
73       * that request from seeing the changes because a reference to the 
74       * configuration is stored in the request and then retrieved from there.
75       * </p>
76       * 
77       * <p>
78       * Passing null to this method returns the current configuration. Subsequent
79       * calls with null are not guarenteed to return the same configuration 
80       * instance.
81       * </p> 
82       *
83       * @param   request (Optional) The ServletRequest used to maintained request
84       *          consistency
85       * @return  The singleton instance
86       */
87      public static ActionFlowConfigRegistry getInstance(ServletRequest   request) {
88          assert (instance != null) : "instance == null";
89  
90          ActionFlowConfigRegistry localInstance = null; 
91          if (request == null) {
92              localInstance = instance;
93          } else {
94              localInstance = (ActionFlowConfigRegistry) request.getAttribute(KEY);
95          }
96          
97          if (localInstance == null && request != null) {
98              request.setAttribute(KEY, instance);
99              localInstance = instance;
100         }
101 
102         return localInstance;
103     }
104 
105     /**
106      * Singleton setter method. This sets a new store instance into the singleton
107      * and it is very important to understand that this change 
108      */
109     protected static void setInstance(ActionFlowConfigRegistry newStore) {
110         assert (newStore != null) : "newStore == null";
111         instance = newStore;
112     }
113 
114 
115     /**
116      * Stores the given Namespace into this store.
117      *
118      * @param   namespace The Namespace to add to the store
119      * @return  The old Namespace that was stored and had the same name
120      *          as the given Namespace or null if one with the same name
121      *          doesn't exist in the store
122      * @throws  IllegalArgumentException If namespace is null
123      */
124     protected Namespace register(Namespace namespace)
125     throws IllegalArgumentException   {
126         if (namespace == null) {
127             throw new IllegalArgumentException  ("The namespace is null");
128         }
129 
130         return (Namespace) namespaces.put(namespace.getName(), namespace);
131     }
132 
133     /**
134      * Finds the Namespace with the given name inside this store.
135      *
136      * @param   name The name of the namespace to locate
137      * @return  The Namespace that was stored under the given name or null
138      *          if one was never stored
139      * @throws  IllegalArgumentException If name is null or empty
140      */
141     public Namespace lookup(String   name) throws IllegalArgumentException   {
142         if (name == null || StringTools.isEmpty(name)) {
143             throw new IllegalArgumentException  ("The name is null or empty");
144         }
145 
146         return (Namespace) namespaces.get(name);
147     }
148 
149     /**
150      * Returns an Iterator over all the Namespaces stored in this ActionFlowConfigRegistry.
151      * This Iterator is NOT live and calling the remove method has no effect
152      * on the ActionFlowConfigRegistry. This Iterator might not reflect the exact values
153      * stored in the ActionFlowConfigRegistry because it is a copy.
154      *
155      * @return  An Iterator over all the Namespaces stored in the ActionFlowConfigRegistry.
156      */
157     public Iterator   iterator() {
158         Map   temp = new HashMap  (namespaces);
159         return temp.values().iterator();
160     }
161 }
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