XSLT Transform in XML Signature: Exception

Question

Hello,
I have following problem with an XSLT tranform in my XML signature. Here is the code I use to add XSLT to signature:
main() {
DOMStructure stylesheet = new DOMStructure( getStylesheet() );
XSLTTransformParameterSpec spec = new XSLTTransformParameterSpec( stylesheet );
transforms.add( fac.newTransform( Transform.XSLT, spec ) );
private Element getStylesheet() throws Exception {
     String stylesheet = //"<?xml version=\"1.0\"?>" +
                    "<xslt:stylesheet version=\"1.0\" xmlns:xslt=\"http://www.w3.org/1999/XSL/Transform\">\n" +
                    " <xsl:include href=\"http://extern XSLT\" />\n" +
                    " <xslt:template match=\"/\">" +
                    " <xsl:apply-imports />" +
                    " </xslt:template>" +
                    "</xslt:stylesheet>\n";
     DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
     //dbf.setValidating( true );
     return dbf.newDocumentBuilder().parse( new ByteArrayInputStream( stylesheet.getBytes() ) ).getDocumentElement();
I get following exception:
javax.xml.crypto.dsig.XMLSignatureException: javax.xml.crypto.dsig.TransformException: com.sun.org.apache.xml.internal.security.transforms.TransformationException: Cannot find xslt:stylesheet in Transform
Original Exception was com.sun.org.apache.xml.internal.security.transforms.TransformationException: Cannot find xslt:stylesheet in Transform
     at org.jcp.xml.dsig.internal.dom.DOMReference.transform(Unknown Source)
     at org.jcp.xml.dsig.internal.dom.DOMReference.digest(Unknown Source)
     at org.jcp.xml.dsig.internal.dom.DOMXMLSignature.digestReference(Unknown Source)
     at org.jcp.xml.dsig.internal.dom.DOMXMLSignature.sign(Unknown Source)
In google I cannot find any details what can be wrong.
Any suggestions?
Thanks in advance,
errno

Answer 1

Thanks for your response. Sorry - I tried both versions with xslt and xsl - doesn't worked -> the error in my post is actually caused through the multiple changes of this part of code. Here once again:
private Element getStylesheet() throws Exception {
          String stylesheet = //"<?xml version=\"1.0\"?>" +
                                   "<xslt:stylesheet version=\"1.0\" xmlns:xslt=\"http://www.w3.org/1999/XSL/Transform\">\n" +
                                   " <xslt:include href=\"external XSLTl\" />\n" +
                                   " <xslt:template match=\"/\">" +
                                   " <xslt:apply-imports />" +
                                   " </xslt:template>" +
                                   "</xslt:stylesheet>\n";
          DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
          //dbf.setValidating( true );
          return dbf.newDocumentBuilder().parse( new ByteArrayInputStream( stylesheet.getBytes() ) ).getDocumentElement();
Thanks,
errno