convert-date: suggestion and implementation

I've found myself needing to convert between various
date formats on a regular basis.  Ideally there would
be a function available in xpath that would allow this:

   convert-date( 
     date-in      <!-- Date string to be converted            -->
     format-in    <!-- Representation of incoming date string -->
     format-out   <!-- Representation of outgoing date string -->
   )

  So that:  convert-date('19991004','yyyyMMdd','EEEE dd MMM yyyy')
  Gives:    Monday 04 Oct 1999

For now, I've implemented it as an external function, via Java.
Any suggestions?  What is the chance of something like this 
being put into xslt or even xpath?

Clark

Oh yes, here is an implementation for jclark's wonderful xt!

....

package com.clarkevans.xtk;

import java.text.*;
import java.util.*;

public class DateConverter {
  public static String convert(
    String dateIn,    // string of date to convert
    String formatIn,  // format of incoming string
    String formatOut  // format of outgoing string 
  )
  {
    try
    { 
      if( "now" == dateIn ) 
      {
        return (new SimpleDateFormat(formatOut).format(new Date()));
      }
      else
      {
        return (new SimpleDateFormat(formatOut)).format(
               (new SimpleDateFormat(formatIn)).parse(
                 dateIn, new ParsePosition(0)));
      }
    }
    catch( Exception e )
    {
      return "";
    }
  }
}


/******** Here is a test stylesheet **************************

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/XSL/Transform/1.0"
  xmlns="http://www.w3.org/TR/REC-html40"
  result-ns="">
     
<xsl:template match="/">
   <xsl:call-template name="convert-date">
     <xsl:with-param name="input-date">19991003</xsl:with-param>
   </xsl:call-template>
</xsl:template>


<xsl:template name="convert-date">
  <xsl:param name="output-format"> EEEE, d MMM yyyy </xsl:param>
  <xsl:param name="input-date">now</xsl:param>
  <xsl:param name="input-format">yyyyMMdd</xsl:param>
  <xsl:value-of 
    xmlns:ts = "http://www.jclark.com/xt/java/com.clarkevans.xtk.DateConverter"
    select   = "ts:convert(string($input-date),
                        string($input-format),
                        string($output-format))" />
</xsl:template>

</xsl:stylesheet>


<!--  Copied from java.text.SimpleDateFormat (c) 1999 Sun Microsystems

    Symbol   Meaning                 Presentation        Example
    ~~~~~~   ~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~
     G        era designator          (Text)              AD
     y        year                    (Number)            1996
     M        month in year           (Text and Number)     July and 07
     d        day in month            (Number)            10
     h        hour in am/pm (1~12)    (Number)            12
     H        hour in day (0~23)      (Number)            0
     m        minute in hour          (Number)            30
     s        second in minute        (Number)            55
     S        millisecond             (Number)            978
     E        day in week             (Text)              Tuesday
     D        day in year             (Number)            189
     F        day of week in month    (Number)            2 (2nd Wed in
July)
     w        week in year            (Number)            27
     W        week in month           (Number)            2
     a        am/pm marker            (Text)              PM
     k        hour in day (1~24)      (Number)            24
     K        hour in am/pm (0~11)    (Number)            0
     z        time zone               (Text)              Pacific Standard
Time
     '        escape for text         (Delimiter)
     ''       single quote            (Literal)           '     

 Format Pattern                         Result
 ~~~~~~~~~~~~~~                         ~~~~~~~~
 "yyyy.MM.dd G 'at' hh:mm:ss z"    ->>  1996.07.10 AD at 15:08:56 PDT
 "EEE, MMM d, ''yy"                ->>  Wed, July 10, '96
 "h:mm a"                          ->>  12:08 PM
 "hh 'o''clock' a, zzzz"           ->>  12 o'clock PM, Pacific Daylight
Time
 "K:mm a, z"                       ->>  0:00 PM, PST
 "yyyyy.MMMMM.dd GGG hh:mm aaa"    ->>  1996.July.10 AD 12:08 PM
     
-->

************************************************************/





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