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  package org.apache.cayenne.project.extension;
  
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.cayenne.CayenneRuntimeException;
  import org.apache.cayenne.configuration.xml.DefaultHandlerFactory;
  import org.apache.cayenne.configuration.xml.NamespaceAwareNestedTagHandler;
  import org.apache.cayenne.di.Inject;
  
  /**
   * Project parser handlers factory that will use third-party extensions
   * to provide handlers for unknown tags.
   *
   * @see ProjectExtension
   * @see DefaultHandlerFactory
   *
   * @since 4.1
   */
  public class ExtensionAwareHandlerFactory extends DefaultHandlerFactory {
  
      Map<String, LoaderDelegate> loaderDelegates = new ConcurrentHashMap<>();
  
      public ExtensionAwareHandlerFactory(@Inject List<ProjectExtension> extensions) {
          for(ProjectExtension extension : extensions) {
              LoaderDelegate delegate = extension.createLoaderDelegate();
              LoaderDelegate old = loaderDelegates.put(delegate.getTargetNamespace(), delegate);
              if(old != null) {
                  throw new CayenneRuntimeException("Found two loader delegates for namespace %s",
                          delegate.getTargetNamespace());
              }
          }
      }
  
      @Override
      public NamespaceAwareNestedTagHandler createHandler(String namespace, String localName,
                                                          NamespaceAwareNestedTagHandler parent) {
  
          LoaderDelegate delegate = loaderDelegates.get(namespace);
          if(delegate != null) {
              NamespaceAwareNestedTagHandler handler = delegate.createHandler(parent, localName);
              if(handler != null) {
                  return handler;
              }
          }
  
          return super.createHandler(namespace, localName, parent);
      }
  }
  