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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          log.debug("Class Fragment is " + name);
    70
    71          if (StringUtils.isNotEmpty(name))
    72          {
    73              for (String p : packages)
    74              {
    75                  StringBuilder sb = new StringBuilder();
    76
    77                  sb.append(p).append('.').append(packageName).append('.').append(name);
    78                  String className = sb.toString();
    79
    80                  log.debug("Trying " + className);
    81
    82                  try
    83                  {
    84                      Class<T> servClass = classCache.get(className);
    85                      if (servClass == null)
    86                      {
    87                          servClass = (Class<T>) Class.forName(className);
    88                          classCache.put(className, servClass);
    89                      }
    90                      assembler = servClass.newInstance();
    91                      break; // for()
    92                  }
    93                  catch (ClassNotFoundException cnfe)
    94                  {
    95                      // Do this so we loop through all the packages.
    96                      log.debug(className + ": Not found");
    97                  }
    98                  catch (NoClassDefFoundError ncdfe)
    99                  {
    100                     // Do this so we loop through all the packages.
    101                     log.debug(className + ": No Class Definition found");
    102                 }
    103                 catch (ClassCastException cce)
    104                 {
    105                     // This means trouble!
    106                     // Alternatively we can throw this exception so
    107                     // that it will appear on the client browser
    108                     log.error("Could not load "+className, cce);
    109                     break; // for()
    110                 }
    111                 catch (InstantiationException ine)
    112                 {
    113                     // This means trouble!
    114                     // Alternatively we can throw this exception so
    115                     // that it will appear on the client browser
    116                     log.error("Could not load "+className, ine);
    117                     break; // for()
    118                 }
    119                 catch (IllegalAccessException ilae)
    120                 {
    121                     // This means trouble!
    122                     // Alternatively we can throw this exception so
    123                     // that it will appear on the client browser
    124                     log.error("Could not load "+className, ilae);
    125                     break; // for()
    126                 }
    127                 // With ClassCastException, InstantiationException we hit big problems
    128             }
    129         }
    130         log.debug("Returning: " + assembler);
    131
    132         return assembler;
    133     }
    134
    135     /**
    136      * Get the loader for this type of assembler
    137      *
    138      * @return a Loader
    139      */
    140     @Override
    141     public abstract Loader<T> getLoader();
    142
    143     /**
    144      * Get the size of a possibly configured cache
    145      *
    146      * @return the size of the cache in bytes
    147      */
    148     @Override
    149     public int getCacheSize()
    150     {
    151         return getLoader().getCacheSize();
    152     }
    153 }