package org.apache.turbine.services.assemblerbroker.util.java;

 /*

  * 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.util.List;

 import java.util.concurrent.ConcurrentHashMap;

 import org.apache.commons.lang.StringUtils;

 import org.apache.commons.logging.Log;

 import org.apache.commons.logging.LogFactory;

 import org.apache.turbine.modules.Assembler;

 import org.apache.turbine.modules.GenericLoader;

 import org.apache.turbine.modules.Loader;

 import org.apache.turbine.services.assemblerbroker.util.AssemblerFactory;

 /**

  * A screen factory that attempts to load a java class from

  * the module packages defined in the TurbineResource.properties.

  *

  * @author <a href="mailto:leon@opticode.co.za">Leon Messerschmidt</a>

  * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>

  * @param <T> the specialized assembler type

  */

 public abstract class JavaBaseFactory<T extends Assembler>

     implements AssemblerFactory<T>

 {

     /** A vector of packages. */

     private static List<String> packages = GenericLoader.getPackages();

     /** Logging */

     protected Log log = LogFactory.getLog(this.getClass());

     /**

      * A cache for previously obtained Class instances, which we keep in order

      * to reduce the Class.forName() overhead (which can be sizable).

      */

     private final ConcurrentHashMap<String, Class<T>> classCache = new ConcurrentHashMap<String, Class<T>>();

     /**

      * Get an Assembler.

      *

      * @param packageName java package name

      * @param name name of the requested Assembler

      * @return an Assembler

      */

     @SuppressWarnings("unchecked")

     public T getAssembler(String packageName, String name)

     {

         T assembler = null;

         if (log.isDebugEnabled())

         {

             log.debug("Class Fragment is " + name);

         }

         if (StringUtils.isNotEmpty(name))

         {

             for (String p : packages)

             {

                 StringBuilder sb = new StringBuilder();

                 sb.append(p).append('.').append(packageName).append('.').append(name);

                 String className = sb.toString();

                 if (log.isDebugEnabled())

                 {

                     log.debug("Trying " + className);

                 }

                 try

                 {

                     Class<T> servClass = classCache.get(className);

                     if (servClass == null)

                     {

                         servClass = (Class<T>) Class.forName(className);

                         Class<T> _servClass = classCache.putIfAbsent(className, servClass);

                         if (_servClass != null)

                         {

                             servClass = _servClass;

                         }

                     }

                     assembler = servClass.newInstance();

                     break; // for()

                 }

                 catch (ClassNotFoundException cnfe)

                 {

                     // Do this so we loop through all the packages.

                     log.debug(className + ": Not found");

                 }

                 catch (NoClassDefFoundError ncdfe)

                 {

                     // Do this so we loop through all the packages.

                     log.debug(className + ": No Class Definition found");

                 }

                 catch (ClassCastException cce)

                 {

                     // This means trouble!

                     // Alternatively we can throw this exception so

                     // that it will appear on the client browser

                     log.error("Could not load "+className, cce);

                     break; // for()

                 }

                 catch (InstantiationException ine)

                 {

                     // This means trouble!

                     // Alternatively we can throw this exception so

                     // that it will appear on the client browser

                     log.error("Could not load "+className, ine);

                     break; // for()

                 }

                 catch (IllegalAccessException ilae)

                 {

                     // This means trouble!

                     // Alternatively we can throw this exception so

                     // that it will appear on the client browser

                     log.error("Could not load "+className, ilae);

                     break; // for()

                 }

                 // With ClassCastException, InstantiationException we hit big problems

             }

         }

         if (log.isDebugEnabled())

         {

             log.debug("Returning: " + assembler);

         }

         return assembler;

     }

     /**

      * Get the loader for this type of assembler

      *

      * @return a Loader

      */

     @Override

     public abstract Loader<T> getLoader();

     /**

      * Get the size of a possibly configured cache

      *

      * @return the size of the cache in bytes

      */

     @Override

     public int getCacheSize()

     {

         return getLoader().getCacheSize();

     }

 }