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   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
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  package org.apache.cayenne.configuration.xml;
  
  import java.util.Objects;
  
  import org.xml.sax.Attributes;
  import org.xml.sax.ContentHandler;
  import org.xml.sax.SAXException;
  
  /**
   * Base class for handlers that can delegate execution of unknown tags to
   * handlers produced by factory.
   *
   * @since 4.1
   */
  abstract public class NamespaceAwareNestedTagHandler extends SAXNestedTagHandler {
  
      protected String targetNamespace;
  
      protected boolean allowAllNamespaces;
  
      private StringBuilder charactersBuffer = new StringBuilder();
  
      public NamespaceAwareNestedTagHandler(LoaderContext loaderContext) {
          super(loaderContext);
      }
  
      public NamespaceAwareNestedTagHandler(SAXNestedTagHandler parentHandler, String targetNamespace) {
          super(parentHandler);
          this.targetNamespace = Objects.requireNonNull(targetNamespace);
      }
  
      public NamespaceAwareNestedTagHandler(NamespaceAwareNestedTagHandler parentHandler) {
          this(parentHandler, parentHandler.targetNamespace);
      }
  
      abstract protected boolean processElement(String namespaceURI, String localName, Attributes attributes) throws SAXException;
  
      protected boolean processCharData(String localName, String data) {
          return false;
      }
  
      @Override
      public void characters(char[] ch, int start, int length) throws SAXException {
          charactersBuffer.append(ch, start, length);
      }
  
      @Override
      public final void startElement(String namespaceURI, String localName,
                                     String qName, Attributes attributes) throws SAXException {
  
          ContentHandler childHandler = createChildTagHandler(namespaceURI, localName, qName, attributes);
  
          boolean validNamespace = allowAllNamespaces || namespaceURI.equals(targetNamespace);
          if(!validNamespace || !processElement(namespaceURI, localName, attributes)) {
              // recursively pass element down into child handlers
              childHandler.startElement(namespaceURI, localName, qName, attributes);
          }
  
          // push child handler to the stack...
          loaderContext.getXmlReader().setContentHandler(childHandler);
          charactersBuffer.delete(0, charactersBuffer.length());
      }
  
      @Override
      public void endElement(String namespaceURI, String localName, String qName) throws SAXException {
          super.endElement(namespaceURI, localName, qName);
          String data = charactersBuffer.toString();
          if(!processCharData(localName, data)) {
              if(namespaceURI.equals(targetNamespace) && parentHandler instanceof NamespaceAwareNestedTagHandler) {
                  ((NamespaceAwareNestedTagHandler)parentHandler).processCharData(localName, data);
              }
          }
      }
  
      @Override
      protected ContentHandler createChildTagHandler(String namespaceURI, String localName,
                                                     String qName, Attributes attributes) {
          // try to pass unknown tags to someone else
          return loaderContext.getFactory().createHandler(namespaceURI, localName, this);
      }
  
      public void setTargetNamespace(String targetNamespace) {
          this.targetNamespace = targetNamespace;
      }
  
      public void setAllowAllNamespaces(boolean allowAllNamespaces) {
          this.allowAllNamespaces = allowAllNamespaces;
      }
  }
  