XSLT - calling Java method - gives: The first argument to the non-static Java function 'doubleIntEcho' is not a valid object reference

Question

From an XSLT stylesheet I would like to call a Java (extention) method.

The error message is:

The first argument to the non-static Java function 'doubleIntEcho' is not a valid object reference.

My simplified POC consists of 4 parts:

1. XML: file

<?xml version="1.0"?>
<value>
    <amount>1</amount>
    <amount>2</amount>
    <amount>3</amount>
</value>

XSLT stylesheet:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:jcall="java:x.y.z.XsltCallingJavaEchoTwice">
    <xsl:output method="xml"/>

    <xsl:template match="/value">
        <value>
            <xsl:apply-templates select="amount"/>
        </value>
    </xsl:template>

    <xsl:template match="amount">
        <xsl:copy>
            <value>
                <xsl:value-of select="text()"/>
            </value>
            <value-int>
                <xsl:value-of select="jcall:doubleIntEcho(number(.))"/>
            </value-int>
            <value-string>
                <xsl:value-of select="jcall:doubleStringEcho(text())"/>
            </value-string>
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>

3. Java class with the extention:

package x.y.z;

public class XsltCallingJavaEchoTwice {
    public static String doubleStringEcho( String input) {
        return "Source=" + input + ", echo=" + input + ", echo2=" + input;
    }
    public static int doubleIntEcho( int input) {
        return input + input;
    }
}

4. The Java environment starting the XSLT transformation process:

public class XsltFilterParentWithAllChildren {

  private static final String XML_FILENAME = "files/xslt-call-java-amounts.xml";
  private static final String XSLT_FILENAME = "files/xslt-call-java-xsl.xsl";
  private static final String XML_OUTPUT_FILENAME = "files/output.xml";

  public static void main(String[] args) {
    deleteFile( XML_OUTPUT_FILENAME);
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    try (InputStream is = new FileInputStream(XML_FILENAME)) {
      DocumentBuilder db = dbf.newDocumentBuilder();
      Document doc = db.parse(is);
      try (FileOutputStream output = new FileOutputStream(XML_OUTPUT_FILENAME)) {
        transform(doc, output);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }   
  private static void transform(Document doc, OutputStream output) throws TransformerException {
    TransformerFactory transformerFactory = TransformerFactory.newInstance();
    Transformer transformer = transformerFactory.newTransformer(
            new StreamSource(new File(XSLT_FILENAME)));
    transformer.transform(new DOMSource(doc), new StreamResult(output));
  }   
  private static void deleteFile( String pathname) {
    new File( pathname).delete();
  }
}

Which JRE/JDK (version), do you rely on the built-in TransformerFactory or have you added Xalan or Saxon to the class path? — Martin Honnen
– Martin Honnen, Commented Jul 23, 2022 at 12:43

Martin Honnen · Accepted Answer · 2022-07-23 13:23:07Z

2

Looking at https://xalan.apache.org/xalan-j/extensions.html#ext-func-calls I would rather expect e.g. xmlns:java="http://xml.apache.org/xalan/java" and then e.g. <xsl:value-of select="java:x.y.z.XsltCallingJavaEchoTwice.doubleIntEcho(number(.))"/>.

answered Jul 23, 2022 at 13:23

Martin Honnen

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2 Comments

tm1701 Over a year ago

There is also a more official method: TransformerFactoryImpl factory = new TransformerFactoryImpl(); factory.getConfiguration().registerExtensionFunction(new MyExtensionFunction());

Martin Honnen Over a year ago

@tm1701, that seems to be part of the Saxon specific API and of course is a different approach, instead of inlining the Java code in the XSLT and using reflexion you precompile your extension in Java. Certainly the cleaner approach in the long run and use it of you know you use Saxon and have to ability to precompile your extension function code. But using reflexion is not less official.

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