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    1   package org.apache.turbine.services.assemblerbroker.util.java;
    2
    3
    4   /*
    5    * Licensed to the Apache Software Foundation (ASF) under one
    6    * or more contributor license agreements.  See the NOTICE file
    7    * distributed with this work for additional information
    8    * regarding copyright ownership.  The ASF licenses this file
    9    * to you under the Apache License, Version 2.0 (the
    10   * "License"); you may not use this file except in compliance
    11   * with the License.  You may obtain a copy of the License at
    12   *
    13   *   http://www.apache.org/licenses/LICENSE-2.0
    14   *
    15   * Unless required by applicable law or agreed to in writing,
    16   * software distributed under the License is distributed on an
    17   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    18   * KIND, either express or implied.  See the License for the
    19   * specific language governing permissions and limitations
    20   * under the License.
    21   */
    22
    23  import java.util.List;
    24  import java.util.concurrent.ConcurrentHashMap;
    25
    26  import org.apache.commons.lang.StringUtils;
    27  import org.apache.commons.logging.Log;
    28  import org.apache.commons.logging.LogFactory;
    29  import org.apache.turbine.modules.Assembler;
    30  import org.apache.turbine.modules.GenericLoader;
    31  import org.apache.turbine.modules.Loader;
    32  import org.apache.turbine.services.assemblerbroker.util.AssemblerFactory;
    33
    34  /**
    35   * A screen factory that attempts to load a java class from
    36   * the module packages defined in the TurbineResource.properties.
    37   *
    38   * @author <a href="mailto:leon@opticode.co.za">Leon Messerschmidt</a>
    39   * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
    40   * @param <T> the specialized assembler type
    41   */
    42  public abstract class JavaBaseFactory<T extends Assembler>
    43      implements AssemblerFactory<T>
    44  {
    45      /** A vector of packages. */
    46      private static List<String> packages = GenericLoader.getPackages();
    47
    48      /** Logging */
    49      protected Log log = LogFactory.getLog(this.getClass());
    50
    51      /**
    52       * A cache for previously obtained Class instances, which we keep in order
    53       * to reduce the Class.forName() overhead (which can be sizable).
    54       */
    55      private final ConcurrentHashMap<String, Class<T>> classCache = new ConcurrentHashMap<String, Class<T>>();
    56
    57      /**
    58       * Get an Assembler.
    59       *
    60       * @param packageName java package name
    61       * @param name name of the requested Assembler
    62       * @return an Assembler
    63       */
    64      @SuppressWarnings("unchecked")
    65      public T getAssembler(String packageName, String name)
    66      {
    67          T assembler = null;
    68
    69          if (log.isDebugEnabled())
    70          {
    71              log.debug("Class Fragment is " + name);
    72          }
    73
    74          if (StringUtils.isNotEmpty(name))
    75          {
    76              for (String p : packages)
    77              {
    78                  StringBuilder sb = new StringBuilder();
    79
    80                  sb.append(p).append('.').append(packageName).append('.').append(name);
    81                  String className = sb.toString();
    82
    83                  if (log.isDebugEnabled())
    84                  {
    85                      log.debug("Trying " + className);
    86                  }
    87
    88                  try
    89                  {
    90                      Class<T> servClass = classCache.get(className);
    91                      if (servClass == null)
    92                      {
    93                          servClass = (Class<T>) Class.forName(className);
    94                          Class<T> _servClass = classCache.putIfAbsent(className, servClass);
    95                          if (_servClass != null)
    96                          {
    97                              servClass = _servClass;
    98                          }
    99                      }
    100                     assembler = servClass.newInstance();
    101                     break; // for()
    102                 }
    103                 catch (ClassNotFoundException cnfe)
    104                 {
    105                     // Do this so we loop through all the packages.
    106                     log.debug(className + ": Not found");
    107                 }
    108                 catch (NoClassDefFoundError ncdfe)
    109                 {
    110                     // Do this so we loop through all the packages.
    111                     log.debug(className + ": No Class Definition found");
    112                 }
    113                 catch (ClassCastException cce)
    114                 {
    115                     // This means trouble!
    116                     // Alternatively we can throw this exception so
    117                     // that it will appear on the client browser
    118                     log.error("Could not load "+className, cce);
    119                     break; // for()
    120                 }
    121                 catch (InstantiationException ine)
    122                 {
    123                     // This means trouble!
    124                     // Alternatively we can throw this exception so
    125                     // that it will appear on the client browser
    126                     log.error("Could not load "+className, ine);
    127                     break; // for()
    128                 }
    129                 catch (IllegalAccessException ilae)
    130                 {
    131                     // This means trouble!
    132                     // Alternatively we can throw this exception so
    133                     // that it will appear on the client browser
    134                     log.error("Could not load "+className, ilae);
    135                     break; // for()
    136                 }
    137                 // With ClassCastException, InstantiationException we hit big problems
    138             }
    139         }
    140
    141         if (log.isDebugEnabled())
    142         {
    143             log.debug("Returning: " + assembler);
    144         }
    145
    146         return assembler;
    147     }
    148
    149     /**
    150      * Get the loader for this type of assembler
    151      *
    152      * @return a Loader
    153      */
    154     @Override
    155     public abstract Loader<T> getLoader();
    156
    157     /**
    158      * Get the size of a possibly configured cache
    159      *
    160      * @return the size of the cache in bytes
    161      */
    162     @Override
    163     public int getCacheSize()
    164     {
    165         return getLoader().getCacheSize();
    166     }
    167 }