package org.codehaus.plexus.component.discovery;
   
   /*
    * Copyright 2001-2006 Codehaus Foundation.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  import java.io.IOException;
  import java.io.Reader;
  import java.net.URL;
  import java.net.URLConnection;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.List;
  
  import org.codehaus.plexus.classworlds.realm.ClassRealm;
  import org.codehaus.plexus.component.repository.ComponentSetDescriptor;
  import org.codehaus.plexus.configuration.PlexusConfigurationException;
  import org.codehaus.plexus.context.Context;
  import org.codehaus.plexus.context.ContextMapAdapter;
  import org.codehaus.plexus.util.IOUtil;
  import org.codehaus.plexus.util.InterpolationFilterReader;
  import org.codehaus.plexus.util.ReaderFactory;
  
  // TODO: this should be a default strategy of searching through classloaders. a discoverer should really not have to be
  // concerned finding a particular resource and how to turn it into a set of component descriptors.
  
  /**
   * @author Jason van Zyl
   */
  public abstract class AbstractResourceBasedComponentDiscoverer implements ComponentDiscoverer {
      protected abstract String getComponentDescriptorLocation();
  
      protected abstract ComponentSetDescriptor createComponentDescriptors(Reader reader, String source, ClassRealm realm)
              throws PlexusConfigurationException;
  
      public List<ComponentSetDescriptor> findComponents(Context context, ClassRealm realm)
              throws PlexusConfigurationException {
          List<ComponentSetDescriptor> componentSetDescriptors = new ArrayList<ComponentSetDescriptor>();
  
          Enumeration<URL> resources;
  
          try {
              resources = realm.getResources(getComponentDescriptorLocation());
          } catch (IOException e) {
              throw new PlexusConfigurationException("Unable to retrieve resources for: "
                      + getComponentDescriptorLocation() + " in class realm: " + realm.getId());
          }
  
          for (URL url : Collections.list(resources)) {
              Reader reader = null;
  
              try {
                  URLConnection conn = url.openConnection();
  
                  conn.setUseCaches(false);
  
                  conn.connect();
  
                  reader = ReaderFactory.newXmlReader(conn.getInputStream());
  
                  InterpolationFilterReader interpolationFilterReader =
                          new InterpolationFilterReader(reader, new ContextMapAdapter(context));
  
                  ComponentSetDescriptor componentSetDescriptor =
                          createComponentDescriptors(interpolationFilterReader, url.toString(), realm);
  
                  componentSetDescriptors.add(componentSetDescriptor);
              } catch (IOException ex) {
                  throw new PlexusConfigurationException("Error reading configuration " + url, ex);
              } finally {
                  IOUtil.close(reader);
              }
          }
  
          return componentSetDescriptors;
      }
  }