ResourceUtils


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61  
62  package org.apache.commons.discovery.tools;
63  
64  import java.io.IOException  ;
65  import java.io.InputStream  ;
66  import java.util.Properties  ;
67  
68  import org.apache.commons.discovery.DiscoveryException;
69  import org.apache.commons.discovery.Resource;
70  import org.apache.commons.discovery.listeners.FirstResourceListener;
71  import org.apache.commons.discovery.resource.ClassLoaders;
72  import org.apache.commons.discovery.resource.DiscoverResources;
73  
74  
75  /**
76   * Mechanisms to locate and load a class.
77   * The load methods locate a class only.
78   * The find methods locate a class and verify that the
79   * class implements an given interface or extends a given class.
80   * 
81   * @author Richard A. Sitze
82   * @author Craig R. McClanahan
83   * @author Costin Manolache
84   */
85  public class ResourceUtils {
86      /**
87       * Get package name.
88       * Not all class loaders 'keep' package information,
89       * in which case Class.getPackage() returns null.
90       * This means that calling Class.getPackage().getName()
91       * is unreliable at best.
92       */
93      public static String   getPackageName(Class   clazz) {
94          Package   clazzPackage = clazz.getPackage();
95          String   packageName;
96          if (clazzPackage != null) {
97              packageName = clazzPackage.getName();
98          } else {
99              String   clazzName = clazz.getName();
100             packageName = new String  (clazzName.toCharArray(), 0, clazzName.lastIndexOf('.'));
101         }
102         return packageName;
103     }
104     
105     
106     /**
107      * Load the resource <code>resourceName</code>.
108      * Try each classloader in succession,
109      * until first succeeds, or all fail.
110      * If all fail and <code>resouceName</code> is not absolute
111      * (doesn't start with '/' character), then retry with
112      * <code>packageName/resourceName</code> after changing all
113      * '.' to '/'.
114      * 
115      * @param resourceName The name of the resource to load.
116      */
117     public static Resource getResource(Class   spi,
118                                        String   resourceName,
119                                        ClassLoaders loaders)
120         throws DiscoveryException
121     {
122         FirstResourceListener listener = new FirstResourceListener();
123         
124         DiscoverResources explorer = new DiscoverResources(loaders);
125         explorer.setListener(listener);
126         explorer.find(resourceName);
127         
128         if (spi != null  &&
129             (listener.getFirst() == null)  &&
130             resourceName.charAt(0) != '/')
131         {
132             /**
133              * If we didn't find the resource, and if the resourceName
134              * isn't an 'absolute' path name, then qualify with
135              * package name of the spi.
136              */
137             explorer.find(getPackageName(spi).replace('.','/') + "/" + resourceName);
138         }
139         
140         return listener.getFirst();
141     }
142     
143     /**
144      * Load named property file, optionally qualifed by spi's package name
145      * as per Class.getResource.
146      * 
147      * A property file is loaded using the following sequence of class loaders:
148      *   <ul>
149      *     <li>Thread Context Class Loader</li>
150      *     <li>DiscoverSingleton's Caller's Class Loader</li>
151      *     <li>SPI's Class Loader</li>
152      *     <li>DiscoverSingleton's (this class) Class Loader</li>
153      *     <li>System Class Loader</li>
154      *   </ul>
155      * 
156      * @param
157      * @param propertiesFileName The property file name.
158      * 
159      * @return Instance of a class implementing the SPI.
160      * 
161      * @exception DiscoveryException Thrown if the name of a class implementing
162      *            the SPI cannot be found, if the class cannot be loaded and
163      *            instantiated, or if the resulting class does not implement
164      *            (or extend) the SPI.
165      */    
166     public static Properties   loadProperties(Class   spi,
167                                             String   propertiesFileName,
168                                             ClassLoaders classLoaders)
169         throws DiscoveryException
170     {
171         Properties   properties = null;
172         
173         if (propertiesFileName != null) {
174             try {
175                 Resource resource = getResource(spi, propertiesFileName, classLoaders);
176                 if (resource != null) {
177                     InputStream   stream = resource.getResourceAsStream();
178         
179                     if (stream != null) {
180                         properties = new Properties  ();
181                         try {
182                             properties.load(stream);
183                         } finally {
184                             stream.close();
185                         }
186                     }
187                 }
188             } catch (IOException   e) {
189                 ;  // ignore
190             } catch (SecurityException   e) {
191                 ;  // ignore
192             }
193         }
194         
195         return properties;
196     }
197 }
198
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