View Javadoc

1   /*****************************************************************
2    * Licensed to the Apache Software Foundation (ASF) under one   *
3    * or more contributor license agreements.  See the NOTICE file *
4    * distributed with this work for additional information        *
5    * regarding copyright ownership.  The ASF licenses this file   *
6    * to you under the Apache License, Version 2.0 (the            *
7    * "License"); you may not use this file except in compliance   *
8    * with the License.  You may obtain a copy of the License at   *
9    *                                                              *
10   *   http://www.apache.org/licenses/LICENSE-2.0                 *
11   *                                                              *
12   * Unless required by applicable law or agreed to in writing,   *
13   * software distributed under the License is distributed on an  *
14   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
15   * KIND, either express or implied.  See the License for the    *
16   * specific language governing permissions and limitations      *
17   * under the License.                                           *
18   ****************************************************************/
19  package org.apache.james.postage.classloading;
20  
21  import java.util.HashMap;
22  import java.util.Map;
23  
24  import org.apache.commons.logging.Log;
25  import org.apache.commons.logging.LogFactory;
26  
27  /***
28   * generic object factory, caching the class object for reuse
29   */
30  public class CachedInstanceFactory {
31  
32      private static Log log = LogFactory.getLog(CachedInstanceFactory.class);
33  
34      private final static Map m_classes = new HashMap();
35  
36      public static Object createInstance(String classname) {
37          Object object = null;
38  
39          Class clazz = null;
40          // class is configured, but not yet loaded
41          if (classname != null && m_classes.get(classname) == null) {
42              try {
43                  clazz = Class.forName(classname);
44              } catch (ClassNotFoundException e) {
45                  log.error("failed to load class " + classname, e);
46              }
47          }
48  
49          // create instance, if custom class is given
50          if (clazz != null) {
51              try {
52                  object = clazz.newInstance();
53              } catch (Exception e) {
54                  log.error("failed to create instance of class " + classname, e);
55              }
56          }
57  
58          return object;
59      }
60  
61  }