SAX.java

/*
 * aitools utilities
 * Copyright (C) 2006 Noel Bush
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.

 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

package org.aitools.util.xml;

import java.util.ArrayList;
import java.util.List;

import javax.xml.XMLConstants;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.aitools.util.runtime.DeveloperError;
import org.apache.log4j.Logger;
import org.apache.xerces.util.XMLCatalogResolver;
import org.jdom.Attribute;
import org.jdom.Namespace;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.XMLReader;

/**
 * Utilities specific to SAX interfaces.
 * 
 * @author <a href="mailto:noel@aitools.org">Noel Bush</a>
 */
public class SAX {

  static {
    System.setProperty("javax.xml.parsers.SAXParserFactory", "org.apache.xerces.jaxp.SAXParserFactoryImpl");
  }
  
  static String XML_SCHEMA_LANGUAGE_PROPERTY = "http://java.sun.com/xml/jaxp/properties/schemaLanguage";
  
  static String XML_SCHEMA_LANGUAGE = "http://www.w3.org/2001/XMLSchema";

  /**
   * Converts a SAX Attributes object to a List of Attribute objects.
   * 
   * @param attributes
   * @return the List of Attribute objects
   */
  public static List<Attribute> getAttributeList(Attributes attributes) {
    int count = attributes.getLength();
    List<Attribute> result = new ArrayList<Attribute>(count);
    for (int index = 0; index < count; index++) {
      // JDOM requires us to jump through this little hoop:
      Namespace namespace;
      String namespaceURI = attributes.getURI(index);
      if (namespaceURI.equals(XMLConstants.XML_NS_URI)) {
        namespace = Namespace.XML_NAMESPACE;
      }
      else {
        namespace = Namespace.getNamespace(namespaceURI);
      }
      result.add(new Attribute(attributes.getLocalName(index), attributes.getValue(index), JDOM
          .getAttributeType(attributes.getType(index)), namespace));
    }
    return result;
  }

  /**
   * Sets up a SAX XML reader that is namespace aware and uses the given feature settings.
   * 
   * @param contentHandler the content handler to attach to the reader.
   * @param logger
   * @param catalogPath 
   * 
   * @return the parser
   */
  public static XMLReader getReader(ContentHandler contentHandler, Logger logger, String catalogPath) {
    
    // Set up a factory and get a parser.
    SAXParserFactory factory = SAXParserFactory.newInstance();
    factory.setNamespaceAware(true);
    factory.setValidating(true);
    factory.setXIncludeAware(true);

    SAXParser parser = null;
    try {
      parser = factory.newSAXParser();
    }
    catch (ParserConfigurationException e) {
      throw new DeveloperError("Error configuring SAXParser created from factory; cannot continue.", e);
    }
    catch (SAXException e) {
      throw new DeveloperError("Error creating SAXParser from factory; cannot continue.", e);
    }
    
    if (parser == null) {
      throw new DeveloperError("SAXParser is null; cannot continue.");
    }
    try {
      parser.setProperty("http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema");
    }
    catch (SAXNotRecognizedException e) {
      assert false: e;
    }
    catch (SAXNotSupportedException e) {
      assert false: e;
    }
    
    // Now get a reader from the parser.
    XMLReader reader = null;
    try {
      reader = parser.getXMLReader();
    }
    catch (SAXException e) {
      throw new DeveloperError("Error creating XMLReader from parser; cannot continue.", e);
    }

    if (reader == null) {
      throw new DeveloperError("XMLReader is null; cannot continue");
    }

    // Next, get an entity resolver that uses the given catalog path, and attach it to the reader.
    XMLCatalogResolver resolver = Resolvers.newXMLCatalogResolver(catalogPath);

    try {
      reader.setProperty("http://apache.org/xml/properties/internal/entity-resolver", resolver);
    }
    catch (SAXNotRecognizedException e) {
      throw new DeveloperError("Property cannot be assigned or retrieved on XMLReader.", e);
    }
    catch (SAXNotSupportedException e) {
      throw new DeveloperError("Requested value cannot be set to given property on XMLReader.", e);
    }
    
    // Finally, attach the given content handler and a basic error handler, and return.
    reader.setContentHandler(contentHandler);
    reader.setErrorHandler(new SimpleSAXErrorHandler(logger));
    return reader;
  }

  /**
   * Renders a given element name and set of attributes as a start tag, including a namespace declaration, if requested.
   * 
   * @param elementName the name of the element to render
   * @param attributes the attributes to include
   * @param includeNamespaceAttribute whether or not to include the namespace attribute
   * @param namespaceURI the namespace URI
   * @return the rendering result
   */
  public static String renderStartTag(String elementName, Attributes attributes, boolean includeNamespaceAttribute,
      String namespaceURI) {
    return JDOM.renderStartTag(elementName, getAttributeList(attributes), includeNamespaceAttribute, namespaceURI);
  }
}