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1   package org.codehaus.plexus.component.discovery;
2   
3   /*
4    * Copyright 2001-2006 Codehaus Foundation.
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    *
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  import java.io.IOException;
20  import java.io.Reader;
21  import java.net.URL;
22  import java.net.URLConnection;
23  import java.util.ArrayList;
24  import java.util.Collections;
25  import java.util.Enumeration;
26  import java.util.List;
27  
28  import org.codehaus.plexus.classworlds.realm.ClassRealm;
29  import org.codehaus.plexus.component.repository.ComponentSetDescriptor;
30  import org.codehaus.plexus.configuration.PlexusConfigurationException;
31  import org.codehaus.plexus.context.Context;
32  import org.codehaus.plexus.context.ContextMapAdapter;
33  import org.codehaus.plexus.util.IOUtil;
34  import org.codehaus.plexus.util.InterpolationFilterReader;
35  import org.codehaus.plexus.util.ReaderFactory;
36  
37  //TODO: this should be a default strategy of searching through classloaders. a discoverer should really not have to be
38  // concerned finding a particular resource and how to turn it into a set of component descriptors.
39  
40  /**
41   * @author Jason van Zyl
42   */
43  public abstract class AbstractResourceBasedComponentDiscoverer
44      implements ComponentDiscoverer
45  {
46      protected abstract String getComponentDescriptorLocation();
47  
48      protected abstract ComponentSetDescriptor createComponentDescriptors( Reader reader, String source, ClassRealm realm )
49          throws PlexusConfigurationException;
50  
51      public List<ComponentSetDescriptor> findComponents( Context context, ClassRealm realm )
52          throws PlexusConfigurationException
53      {
54          List<ComponentSetDescriptor> componentSetDescriptors = new ArrayList<ComponentSetDescriptor>();
55  
56          Enumeration<URL> resources;
57          
58          try
59          {
60              resources = realm.getResources( getComponentDescriptorLocation() );
61          }
62          catch ( IOException e )
63          {
64              throw new PlexusConfigurationException( "Unable to retrieve resources for: " + getComponentDescriptorLocation() + " in class realm: " + realm.getId() );
65          }
66  
67          for ( URL url : Collections.list( resources ))
68          {
69              Reader reader = null;
70              
71              try
72              {
73                  URLConnection conn = url.openConnection();
74  
75                  conn.setUseCaches( false );
76  
77                  conn.connect();
78  
79                  reader = ReaderFactory.newXmlReader( conn.getInputStream() );
80  
81                  InterpolationFilterReader interpolationFilterReader = new InterpolationFilterReader( reader, new ContextMapAdapter( context ) );
82  
83                  ComponentSetDescriptor componentSetDescriptor = createComponentDescriptors( interpolationFilterReader, url.toString(), realm );
84  
85                  componentSetDescriptors.add( componentSetDescriptor );
86              }
87              catch ( IOException ex )
88              {
89                  throw new PlexusConfigurationException( "Error reading configuration " + url, ex );
90              }
91              finally
92              {
93                  IOUtil.close( reader );
94              }
95          }
96  
97          return componentSetDescriptors;
98      }
99  }