ClassesPreloadManager


1   package org.jahia.bin;
2   
3   import java.io.File  ;
4   import java.io.IOException  ;
5   
6   import java.util.ArrayList  ;
7   import java.util.Iterator  ;
8   
9   import org.apache.commons.digester.Digester;
10  import org.apache.commons.digester.Rule;
11  import org.xml.sax.SAXException  ;
12  
13  /**
14   * <p>Title: A manager class that preloads classes into memory for a given
15   * configuration loaded from an XML file </p>
16   * <p>Description: This class is used to preload classes into the default
17   * class loader in order to statisfy static dependencies between Jahia's
18   * classes. This allows us to use our factory pattern that is used notably
19   * in the ObjectKey and ContentObject class hierarchies, that use static
20   * initializers to register class names into the factories.</p>
21   * <p>Copyright: Copyright (c) 2002</p>
22   * <p>Company: </p>
23   * @author Serge Huber
24   * @version 1.0
25   */
26  
27  class ClassesPreloadManager {
28  
29      ArrayList   preloadClassNames = new ArrayList  ();
30  
31      /**
32       * Constructor for the manager. This constructor actually does all the work
33       * of parsing the configuration file that contains the list of classes to
34       * preload into the default class loader, and then actually calls the
35       * class loader to load the classes, and therefore also call all the static
36       * initializers of those classes.
37       *
38       * The format of the XML file can be seen in this example :
39       * <?xml version="1.0" encoding="ISO-8859-1"?>
40       * <preload-classes>
41       *   <class-name>org.jahia.content.ObjectKey</class-name>
42       *   <class-name>org.jahia.content.ContentFieldKey</class-name>
43       *   <class-name>org.jahia.content.ContentContainerListKey</class-name>
44       *   <class-name>org.jahia.content.ContentObject</class-name>
45       * </preload-classes>
46       *
47       * @param configurationFileName the name of the XML configuration file that
48       * contains a simple list of classes to preload into the default class
49       * loader.
50       *
51       * @throws IOException thrown if there was an IO error while reading or
52       * opening the given XML configuration file
53       * @throws SAXException thrown if there was an XML error while parsing the
54       * configuration file
55       * @throws ClassNotFoundException thrown if one of the classes given in the
56       * configuration file couldn't be found by the default class loader.
57       */
58      public ClassesPreloadManager(String   configurationFileName)
59          throws IOException  , SAXException  , ClassNotFoundException   {
60          loadXMLConfiguration(configurationFileName);
61          preloadClasses();
62      }
63  
64      private void loadXMLConfiguration (String   configurationFileName)
65          throws IOException  , SAXException   {
66  
67          Digester digester = new Digester();
68  
69          // This set of rules calls the addClassName method and passes
70          // in a single parameter to the method.
71          digester.addRule("preload-classes/class-name", new AddClassNameRule());
72  
73          // This method starts the parsing of the document.
74          File   configurationFile = new File  (configurationFileName);
75          digester.parse(configurationFile);
76      }
77  
78      private void preloadClasses()
79          throws ClassNotFoundException   {
80          // we can now actually preload the classes into the default class
81          // loader.
82          Iterator   preloadClassNameIter = preloadClassNames.iterator();
83          while (preloadClassNameIter.hasNext()) {
84              String   curClassName = (String  ) preloadClassNameIter.next();
85              Class.forName(curClassName);
86          }
87      }
88  
89      final class AddClassNameRule extends Rule {
90          public void body(String   namespace, String   name, String   text)
91                  throws Exception   {
92              preloadClassNames.add(text);
93          }
94      }
95  
96  }
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