Source for gnu.xml.pipeline.XsltFilter

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: }