/*

  * This software is licensed under the Apache License, Version 2.0

  * (the "License") agreement; 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 net.admin4j.dao.xml;

 import java.beans.XMLDecoder;

 import java.io.BufferedInputStream;

 import java.io.File;

 import java.io.FileInputStream;

 import net.admin4j.util.Admin4jRuntimeException;

 import org.slf4j.Logger;

 import org.slf4j.LoggerFactory;

 public abstract class BaseDAOXml {

     private Logger logger = LoggerFactory.getLogger(this.getClass());

     protected void versionOutputFile(String xmlFileName, String tempFileName,

             String previousFileName) {

         File file;

         // Rename configured Xml file to .previous

         file = new File(previousFileName);

         if (file.exists()) {

             file.delete();

         }

         file = new File(xmlFileName);

         if (file.exists()) {

             file.renameTo(new File(previousFileName));

         }

         // Rename .temp file to configured Xml File Name

         file = new File(tempFileName);

         file.renameTo(new File(xmlFileName));

     }

     protected String derivePreviousFileName(String xmlFileName) {

         return xmlFileName + ".previous";

     }

     protected Object readXmlFile(String xmlFileName) {

         Object result = null;

         XMLDecoder decoder = null;

         boolean exceptionThrown = false;

         /*

          * Note: classloader assigning business to work around JDK bug

          * http://bugs.sun.com/view_bug.do?bug_id=6329581

          */

         ClassLoader currentContextLoader = Thread.currentThread().getContextClassLoader();

         try {

             Thread.currentThread().setContextClassLoader(this.getClass().getClassLoader());

             DefaultExceptionListener errorListener = new DefaultExceptionListener(xmlFileName);

             decoder = new XMLDecoder(

                 new BufferedInputStream(

                     new FileInputStream(xmlFileName)));

             decoder.setExceptionListener(errorListener);

             try {result = decoder.readObject();}

             catch (Exception e) {

                 logger.error("Error reading file " + xmlFileName, e);

                 exceptionThrown = true;

             }

             if (errorListener.isError() || exceptionThrown) {

                 exceptionThrown = false;

                 String previousFileName = derivePreviousFileName(xmlFileName);

                 errorListener = new DefaultExceptionListener(previousFileName);

                 decoder = new XMLDecoder(

                         new BufferedInputStream(

                             new FileInputStream(previousFileName)));

                 decoder.setExceptionListener(errorListener);

                 try {result = decoder.readObject();}

                 catch (Exception e) {

                     logger.error("Error reading file " + previousFileName, e);

                     exceptionThrown = true;

                 }

                 if (errorListener.isError() || exceptionThrown) {

                     Admin4jRuntimeException ae = new Admin4jRuntimeException("Error reading xml Input after two attempts");

                     ae.addContextValue("xmlFileName", xmlFileName);

                     ae.addContextValue("previousFileName", previousFileName);

                     throw ae;

                 }

                 else {

                     logger.warn("Error reading xmlFile {}.  Back up copy used.", xmlFileName);

                 }

             }

         }

         catch (Throwable t) {

             throw new Admin4jRuntimeException("Error reading XML Exception Information.", t)

                 .addContextValue("xmlFileName", xmlFileName);

         }

         finally {

             if (decoder != null) decoder.close();

             Thread.currentThread().setContextClassLoader(currentContextLoader);

         }

         return result;

     }

 }