XSLTTemplateCache


1   package de.webman.util.xslt;
2   
3   import java.io.File  ;
4   import java.util.Hashtable  ;
5   import javax.xml.transform.ErrorListener  ;
6   import javax.xml.transform.Transformer  ;
7   import javax.xml.transform.TransformerFactory  ;
8   import javax.xml.transform.TransformerException  ;
9   import javax.xml.transform.stream.StreamSource  ;
10  
11  /**
12   * Implementierung eines simplen XSL-Transformer-Caches.
13   *
14   * @author  $Author: uli $
15   * @version $Revision: 1.1 $
16   */
17  public class XSLTTemplateCache
18  {
19  
20      // $Id: XSLTTemplateCache.java,v 1.1 2001/09/10 14:32:49 uli Exp $
21  
22      // Constants.
23  
24      /**
25       * The stylesheet template cache.
26       */
27      private static Hashtable   cache = new Hashtable  ();
28  
29      /**
30       * The modification date cache.
31       */
32      private static Hashtable   dates = new Hashtable  ();
33  
34      /**
35       * The error listener.
36       */
37      private static ErrorListener   ERROR_LISTENER = null;
38  
39      /**
40       * The transformer factory.
41       */
42      private static TransformerFactory   TRANSFORMER_FACTORY = null;
43  
44  
45      // Static access.
46  
47      /**
48       * Returns the error listener.
49       *
50       * @return the error listener.
51       */
52      public static synchronized ErrorListener   getErrorListener ()
53      {
54          if (ERROR_LISTENER == null)
55          {
56              // Lazy initialization.
57              ERROR_LISTENER = new XSLTErrorListener();
58          }
59  
60          return ERROR_LISTENER;
61      }
62  
63      /**
64       * Returns the transformer factory.
65       *
66       * @return the transformer factory.
67       */
68      public static synchronized TransformerFactory   getTransformerFactory ()
69      {
70          if (TRANSFORMER_FACTORY == null)
71          {
72              // Lazy initialization.
73              TRANSFORMER_FACTORY = TransformerFactory.newInstance();
74              TRANSFORMER_FACTORY.setErrorListener(getErrorListener());
75          }
76  
77          return TRANSFORMER_FACTORY;
78      }
79  
80      /**
81       * Returns a transformer for the specified stylesheet.
82       *
83       * @param name the absolute file name of the stylesheet.
84       * @return a transformer for the specified stylesheet.
85       */
86      public static synchronized Transformer   getTransformer (String   name)
87          throws TransformerException  
88      {
89          // Optimistic initialization.
90          Transformer   transformer = (Transformer  ) cache.get(name);
91  
92          // Check file date.
93          File   file = new File  (name);
94          Long   lastModified = new Long  (file.lastModified());
95          Long   cacheModified = (Long  ) dates.get(name);
96  
97          if (! lastModified.equals(cacheModified))
98          {
99              // Cache dirty or empty.
100             transformer = getTransformerFactory().newTransformer(new StreamSource  (file));
101             transformer.setErrorListener(getErrorListener());
102 
103             dates.put(name, lastModified);
104             cache.put(name, transformer);
105         }
106 
107         return transformer;
108     }
109 
110 }
111
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