I'm tring to use a value in a specific tag as variable name. But while converting xml system gives Undeclared variable in XPath expression Exception.
My Xml file is
<request>
<entityType>individual</entityType>
</request>
And Xslt file is
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
exclude-result-prefixes="xs math"
version="3.0">
<xsl:param name="individual" static="yes" as="xs:string" select="'1'"/>
<xsl:param name="legal" static="yes" as="xs:string" select="'2'"/>
<xsl:template match="/*">
<xsl:param name="entity" as="xs:string" select="concat('$',entityType)"/>
<xsl:variable name="input" as="xs:string">
<xsl:evaluate xpath="$entity"/>
</xsl:variable>
<HTML><TITLE><xsl:value-of select="$input"/></TITLE></HTML>
</xsl:template>
</xsl:stylesheet>
i expect the result as
<HTML><TITLE>1</TITLE></HTML>
But I get "Static error in XPath expression supplied to xsl:evaluate: Undeclared variable in XPath expression" message.
If you read https://www.w3.org/TR/xslt-30/#dynamic-xpath then you will find it clearly states "Variables declared in the stylesheet in xsl:variable or xsl:param elements are not in-scope within the target expression.". You will have to use xsl:with-param inside the xsl:evaluate and/or with-params on the xsl:evaluate to declare the parameters you need.
<xsl:evaluate xpath="$entity" with-params="map{ QName('', 'individual') : $individual }"/>
As pointed out in your comment, you want to map certain string color values to integer color values, that might be possible in XSLT 3 with a map e.g. with an input of
<colors>
<color>red</color>
<color>green</color>
</colors>
and an XSLT 3.0 of e.g.
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="3.0"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="#all"
expand-text="yes">
<xsl:param name="color-map"
as="map(xs:string, xs:integer)"
select="map {
'red' : 1,
'green' : 2
}"/>
<xsl:template match="color">
<xsl:copy>{$color-map(.)}</xsl:copy>
</xsl:template>
<xsl:mode on-no-match="shallow-copy"/>
</xsl:stylesheet>
you would get a result of e.g.
<colors>
<color>1</color>
<color>2</color>
</colors>