EntityResolvingSource.java

/* $HeadURL::                                                                                     $
 * $Id$
 *
 * Copyright (c) 2006-2010 by Public Library of Science
 * http://plos.org
 * http://ambraproject.org
 *
 * 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.
 */
package org.ambraproject.xml.transform;

import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.Source;
import javax.xml.transform.sax.SAXSource;

import org.xml.sax.helpers.XMLReaderFactory;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;
import org.xml.sax.SAXException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Creates a {@link Source} that can be used in a {@link javax.xml.transform.Transformer#transform}
 * call with a custom entity resolver.
 *
 * @author Eric Brown and Ronald Tschalär
 * @version $Id$
 */
public class EntityResolvingSource extends SAXSource implements Source {
  private static final Logger log = LoggerFactory.getLogger(EntityResolvingSource.class);
  private static final String xmlReaderCName;

  static {
    /* Remember the name of the XMLReader class so we can use it in the XMLReaderFactory
     * call. Note that we don't set the org.xml.sax.driver property because there seem to
     * be cases where that property is removed again.
     */
    String cname = null;
    try {
      cname = SAXParserFactory.newInstance().newSAXParser().getXMLReader().getClass().getName();
      log.info("Using XMLReader: " + cname);
    } catch (Exception e) {
      log.warn("Failed to get the XMLReader class", e);
    }
    xmlReaderCName = cname;
  }

  /**
   * Construct a new EntityResolvingSource object.
   *
   * @param src is the source of the XML document
   * @param resolver is the custom resolver
   * @throws SAXException if we're unable to create an XMLReader (Should never happen
   *         unless there is a serious initialization problem that is likely the result
   *         of a mis-configuration of the JDK. Multiple errors will likely be logged.)
   */
  public EntityResolvingSource(InputSource src, EntityResolver resolver) throws SAXException {
    super(createXMLReader(resolver), src);
    if (log.isDebugEnabled())
      log.debug("Created " + this.getClass().getName() + " w/" + resolver.getClass().getName());
  }

  private static XMLReader createXMLReader(EntityResolver resolver) throws SAXException {
    try {
      XMLReader rdr = XMLReaderFactory.createXMLReader(xmlReaderCName);
      rdr.setEntityResolver(resolver);
      return rdr;
    } catch (SAXException se) {
      log.error("Unable to create XMLReader from " + xmlReaderCName, se);
      throw se;
    }
  }
}