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61
62 package org.apache.commons.discovery.jdk;
63
64 import java.util.Enumeration JavaDoc;
65 import java.io.IOException JavaDoc;
66
67
68 /**
69  * @author Richard A. Sitze
70  */
71 class JDK11Hooks extends JDKHooks {
72     private static final ClassLoader JavaDoc systemClassLoader
73         = new PsuedoSystemClassLoader();
74
75
76     /**
77      * The thread context class loader is available for JDK 1.2
78      * or later, if certain security conditions are met.
79      *
80      * @return The thread context class loader, if available.
81      * Otherwise return null.
82      */
83     public ClassLoader JavaDoc getThreadContextClassLoader() {
84         return null;
85     }
86     
87     /**
88      * The system class loader is available for JDK 1.2
89      * or later, if certain security conditions are met.
90      *
91      * @return The system class loader, if available.
92      * Otherwise return null.
93      */
94     public ClassLoader JavaDoc getSystemClassLoader() {
95         return systemClassLoader;
96     }
97
98     /**
99      * Implement ClassLoader.getResources for JDK 1.1
100      *
101      * On JDK1.1 there is no getResources() method. We emulate this by
102      * using introspection and doing the lookup ourself, using the list
103      * of URLs, via getURLs().
104      */
105     public Enumeration JavaDoc getResources(ClassLoader JavaDoc loader,
106                                     String JavaDoc resourceName)
107         throws IOException JavaDoc
108     {
109         /**
110          * The simple answer is/was:
111          * return loader.getResources(resourceName);
112          *
113          * However, some classloaders overload the behavior of getResource
114          * (loadClass, etc) such that the order of returned results changes
115          * from normally expected behavior.
116          *
117          * Example: locate classes/resources from child ClassLoaders first,
118          * parents last (in some J2EE environs).
119          *
120          * The resource returned by getResource() should be the same as the
121          * first resource returned by getResources(). Unfortunately, this
122          * is not, and cannot be: getResources() is 'final' in the current
123          * JDK's (1.2, 1.3, 1.4).
124          *
125          * To address this, the implementation of this method will
126          * return an Enumeration such that the first element is the
127          * results of getResource, and all trailing elements are
128          * from getResources. On each iteration, we check so see
129          * if the resource (from getResources) matches the first resource,
130          * and eliminate the redundent element.
131          */
132         
133         final URL first = (URL)loader.getResource(resourceName);
134         final Enumeration JavaDoc rest = loader.getResources(resourceName);
135         
136         return new Enumeration JavaDoc() {
137             private boolean firstDone = (first == null);
138             private URL next = getNext();
139             
140             public Object JavaDoc nextElement() {
141                 URL o = next;
142                 next = getNext();
143                 return o;
144             }
145
146             public boolean hasMoreElements() {
147                 return next != null;
148             }
149             
150             private URL getNext() {
151                 URL n;
152                 
153                 if (!firstDone) {
154                     /**
155                      * First time through, use results of getReference()
156                      * if they were non-null.
157                      */
158                     firstDone = true;
159                     n = first;
160                 } else {
161                     /**
162                      * Subsequent times through,
163                      * use results of getReferences()
164                      * but take out anything that matches 'first'.
165                      *
166                      * Iterate through list until we find one that
167                      * doesn't match 'first'.
168                      */
169                     n = null;
170                     while (rest.hasMoreElements() && n == null) {
171                         n = (URL)rest.nextElement();
172                         if (first != null &&
173                             n != null &&
174                             n.equals(first))
175                         {
176                             n = null;
177                         }
178                     }
179                 }
180                 
181                 return n;
182             }
183         };
184     }
185 }
186
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