How to write xslt extended method? Can you give an example?

What you want to do does not even require a customized java extention. Simply using java.util.Date is enough. However, if you want to format you date string properly, then you do need to write your own class.

I found some time, and wrote 2 examples. One does what you wanted to do. The other does more.

• A simple Java extension example
  You can apply it to any well-formed XML file. It is not a very good practice, since you must use transformer knowing Java. The better practice would be using Microsoft msxml. However, I need to learn it before giving an example. The next FAQ allows you to change the date string format in your XSLT. <h5>XSLT sourece </h5>

  <xsl:stylesheet version="1.0" 
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:java="java">
    <!-- add a today-date to your XML under the root -->
    <xsl:template match="/*">
      <xsl:element name="{name(.)}">
        <today-date>
          <xsl:value-of select="java:util.Date.new()" />
        </today-date>
        <xsl:apply-templates />
      </xsl:element>
    </xsl:template>
  
    <!-- identity template -->
    <xsl:template match="@*|node()">
        <xsl:copy>
          <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>
    </xsl:template>
  </xsl:stylesheet>

• A customized Java extension example
  You can apply it to any well-formed XML file. The date string format can be provided by <xsl:param> if desired. <h5>XSLT sourece </h5>

  <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
    xmlns:xobj="com.example.XObj" 
    version ="1.0">
    <!--<xsl:variable name="contextObj" select="xobj:new(.)" />-->
    <xsl:template match = "@*|node()">
      <xsl:copy>
        <xsl:apply-templates select = "@*|node()"/>
      </xsl:copy>
    </xsl:template>
    <xsl:template match="/*">
      <xsl:element name="{name(.)}" >
        <xsl:element name = "today-date">
          <xsl:value-of select="xobj:getDateString('EEE, MMM d, yyyy')" /> 
        </xsl:element>
        <xsl:apply-templates />
      </xsl:element>
    </xsl:template>
  </xsl:stylesheet>

  <h5>Java Code</h5>

  package com.example;
  import java.util.Date;
  import java.text.SimpleDateFormat;
  public class XObj {
    public static String getDateString(String format) {
      SimpleDateFormat df = new SimpleDateFormat(format);
      return df.format(new Date());
    }
  }

Enjoy!!!