libjava/gnu/xml/pipeline/XsltFilter.java

   1 /* XsltFilter.java --
   2    Copyright (C) 2001 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package gnu.xml.pipeline;
  39
  40 import java.io.IOException;
  41
  42 import javax.xml.transform.TransformerFactory;
  43 import javax.xml.transform.TransformerConfigurationException;
  44 import javax.xml.transform.sax.*;
  45 import javax.xml.transform.stream.StreamSource;
  46
  47 import org.xml.sax.SAXException;
  48 import org.xml.sax.ext.LexicalHandler;
  49
  50
  51 /**
  52  * Packages an XSLT transform as a pipeline component.
  53  * Note that all DTD events (callbacks to DeclHandler and DTDHandler
  54  * interfaces) are discarded, although XSLT transforms may be set up to
  55  * use the LexicalHandler to write DTDs with only an external subset.
  56  * Not every XSLT engine will necessarily be usable with this filter,
  57  * but current versions of
  58  * <a href="http://saxon.sourceforge.net">SAXON</a> and
  59  * <a href="http://xml.apache.org/xalan-j">Xalan</a> should work well.
  60  *
  61  * @see TransformerFactory
  62  *
  63  * @author David Brownell
  64  */
  65 final public class XsltFilter extends EventFilter
  66 {
  67     /**
  68      * Creates a filter that performs the specified transform.
  69      * Uses the JAXP 1.1 interfaces to access the default XSLT
  70      * engine configured for in the current execution context,
  71      * and parses the stylesheet without custom EntityResolver
  72      * or ErrorHandler support.
  73      *
  74      * @param stylesheet URI for the stylesheet specifying the
  75      *  XSLT transform
  76      * @param next provides the ContentHandler and LexicalHandler
  77      *  to receive XSLT output.
  78      * @exception SAXException if the stylesheet can't be parsed
  79      * @exception IOException if there are difficulties
  80      *  bootstrapping the XSLT engine, such as it not supporting
  81      *  SAX well enough to use this way.
  82      */
  83     public XsltFilter (String stylesheet, EventConsumer next)
  84     throws SAXException, IOException
  85     {
  86         // First, get a transformer with the stylesheet preloaded
  87         TransformerFactory      tf = null;
  88         TransformerHandler      th;
  89
  90         try {
  91             SAXTransformerFactory       stf;
  92
  93             tf = TransformerFactory.newInstance ();
  94             if (!tf.getFeature (SAXTransformerFactory.FEATURE)  // sax inputs
  95                     || !tf.getFeature (SAXResult.FEATURE)       // sax outputs
  96                     || !tf.getFeature (StreamSource.FEATURE)    // stylesheet
  97                     )
  98                 throw new IOException ("XSLT factory ("
  99                     + tf.getClass ().getName ()
 100                     + ") does not support SAX");
 101             stf = (SAXTransformerFactory) tf;
 102             th = stf.newTransformerHandler (new StreamSource (stylesheet));
 103         } catch (TransformerConfigurationException e) {
 104             throw new IOException ("XSLT factory ("
 105                 + (tf == null
 106                         ? "none available"
 107                         : tf.getClass ().getName ())
 108                 + ") configuration error, "
 109                 + e.getMessage ()
 110                 );
 111         }
 112
 113         // Hook its outputs up to the pipeline ...
 114         SAXResult               out = new SAXResult ();
 115
 116         out.setHandler (next.getContentHandler ());
 117         try {
 118             LexicalHandler      lh;
 119             lh = (LexicalHandler) next.getProperty (LEXICAL_HANDLER);
 120             out.setLexicalHandler (lh);
 121         } catch (Exception e) {
 122             // ignore
 123         }
 124         th.setResult (out);
 125
 126         // ... and make sure its inputs look like ours.
 127         setContentHandler (th);
 128         setProperty (LEXICAL_HANDLER, th);
 129     }
 130 }