package org.apache.torque.engine.database.transform;

 /*

  * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE

  * file 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 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.InputStream;

 import org.apache.commons.logging.Log;

 import org.apache.commons.logging.LogFactory;

 import org.xml.sax.EntityResolver;

 import org.xml.sax.InputSource;

 import org.xml.sax.SAXException;

 /**

  * A resolver to get the database.dtd file for the XML parser from the jar.

  * 

  * @author <a href="mailto:mpoeschl@marmot.at">Martin Poeschl</a>

  * @author <a href="mailto:kschrader@karmalab.org">Kurt Schrader</a>

  * @author <a href="mailto:quintonm@bellsouth.net">Quinton McCombs</a>

  * @version $Id: DTDResolver.java,v 1.1 2007-10-21 07:57:26 abyrne Exp $

  */

 public class DTDResolver implements EntityResolver {

     /** Where the DTD is located on the web. */

     public static final String WEB_SITE_DTD = "http://db.apache.org/torque/dtd/database_3_3.dtd";

     /** Where the 3.2 DTD is located on the web. */

     public static final String WEB_SITE_DTD_3_2 = "http://db.apache.org/torque/dtd/database_3_2.dtd";

     /** Logging class from commons.logging */

     private static Log log = LogFactory.getLog(DTDResolver.class);

     /**

      * constructor

      */

     public DTDResolver() throws SAXException {

     }

     /**

      * An implementation of the SAX <code>EntityResolver</code> interface to be called by the XML parser. If the dtd is

      * the current Torque DTD, the DTD is read from the generator jar. In all other cases, null is returned to indicate

      * that the parser should open a regular connection to the systemId URI.

      * 

      * @param publicId

      *            The public identifier of the external entity

      * @param systemId

      *            The system identifier of the external entity

      * @return An <code>InputSource</code> for the <code>database.dtd</code> file in the generator jar, or null.

      */

     public InputSource resolveEntity(String publicId, String systemId) throws IOException, SAXException {

         if (WEB_SITE_DTD.equals(systemId)) {

             return readFromClasspath("database.dtd");

         } else if (WEB_SITE_DTD_3_2.equals(systemId)) {

             return readFromClasspath("database_3_2.dtd");

         } else {

             log.debug("Resolver: used default behaviour");

             return null;

         }

     }

     /**

      * Reads the resource with the given name from the classpath.

      * 

      * @param resourceName

      *            the name of the resource to read

      * @return an Inputsource witht the content of the resource.

      * 

      * @throws SAXException

      *             if the resource cannot be read.

      */

     private InputSource readFromClasspath(String resourceName) throws SAXException {

         try {

             InputStream dtdStream = getClass().getResourceAsStream(resourceName);

             // getResource was buggy on many systems including Linux,

             // OSX, and some versions of windows in jdk1.3.

             // getResourceAsStream works on linux, maybe others?

             if (dtdStream != null) {

                 String pkg = getClass().getName().substring(0, getClass().getName().lastIndexOf('.'));

                 log.debug("Resolver: used " + resourceName + " from '" + pkg + "' package");

                 return new InputSource(dtdStream);

             } else {

                 log.warn("Could not locate database.dtd");

                 return null;

             }

         } catch (Exception ex) {

             throw new SAXException("Could not get stream for " + resourceName, ex);

         }

     }

 }