XSLT recursive substitution of string parameters - xslt

Question

I am quite new to XSLT,
I have a source XML message, which in its simplified version looks something like this:
<?xml version='1.0' encoding='iso-8859-1'?>
<Message>
<Invalid>
<InvalidBody>
<SynchError>
<ErrorText>The value of %1 should not be %2.</ErrorText>
<ErrorParameter>
<!-- Error Parameter is %1 identifier -->
<ErrorParameterType>value</ErrorParameterType>
<ErrorParameterValue>someField</ErrorParameterValue>
</ErrorParameter>
<ErrorParameter>
<!-- Error Parameter is %2 identifier -->
<ErrorParameterType>value</ErrorParameterType>
<ErrorParameterValue>someValue</ErrorParameterValue>
</ErrorParameter>
</SynchError>
</InvalidBody>
</Invalid>
</Message>
Now, I would like to use XSLT 1.0 to extract the ErrorText string and substitute the parameters %1 and %2 with the corresponding ErrorParameter/ErrorParameterValue values. The number of parameters %1, %2, %3... cannot be known in advance, so the solution should be flexible enough to accommodate a variable number of parameters.
Is there any elegant way to do this?

Answer 1

So, after quite a lot of googling around and a healthy dose of headache, I came up with the following solution, which seems to work like a charm:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:template match="/">
<xsl:variable name="err-text" select="/Message/Invalid/InvalidBody/SynchError/ErrorText" />
<xsl:variable name="param-count" select="count(/Message/Invalid/InvalidBody/SynchError/ErrorParameter)" />
<xsl:call-template name="replace-params">
<xsl:with-param name="position" select="$param-count"/>
<xsl:with-param name="source-text" select="$err-text" />
</xsl:call-template>
</xsl:template>
<xsl:template name="replace-params">
<xsl:param name="position"/>
<xsl:param name="source-text"/>
<xsl:choose>
<xsl:when test="$position = 0">
<xsl:value-of select="$source-text"/>
</xsl:when>
<xsl:otherwise>
<xsl:call-template name="replace-params">
<xsl:with-param name="position" select="$position - 1"/>
<xsl:with-param name="source-text">
<xsl:call-template name="string-replace-all">
<xsl:with-param name="text" select="$source-text" />
<xsl:with-param name="replace" select="concat('%', $position)" />
<xsl:with-param name="by" select="/Message/Invalid/InvalidBody/SynchError/ErrorParameter[$position]/ErrorParameterValue" />
</xsl:call-template>
</xsl:with-param>
</xsl:call-template>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template name="string-replace-all">
<xsl:param name="text" />
<xsl:param name="replace" />
<xsl:param name="by" />
<xsl:choose>
<xsl:when test="contains($text, $replace)">
<xsl:value-of select="substring-before($text,$replace)" />
<xsl:value-of select="$by" />
<xsl:call-template name="string-replace-all">
<xsl:with-param name="text"
select="substring-after($text,$replace)" />
<xsl:with-param name="replace" select="$replace" />
<xsl:with-param name="by" select="$by" />
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$text" />
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>
I use the "string-replace-all" template as a substitute for the XSLT 2.0 replace() function, since I cannot exclude multiple occurrences of a single parameter.
The "replace-params" template is applied recursively on the original text, iterating backwards on the index of the set of ErrorParameters.

Answer 2

The way I have tackled similar problems is to create a named template that recurses through the string (text element of) <ErrorText> with each cycle picking out the first n% item, then dereferences the <ErrorParameter> to access the contents of that and store in a result, then snip off the n% item just process and calls itself to grab the next one. When there are no more %n items left, return the result.
Here's an example of that, this template basically counts comma-separated items in a parameter passed in on the first cycle called List, and returns a $Count when it's finished.
<xsl:template name="CountList">
<xsl:param name="List"/>
<xsl:param name="Count" select="0"/>
<xsl:choose>
<xsl:when test="contains($List,',') = false()">
<xsl:value-of select="$Count"/>
</xsl:when>
<xsl:otherwise>
<xsl:call-template name="CountList">
<xsl:with-param name="List">
<xsl:value-of select="substring-after($List,',')"/>
</xsl:with-param>
<xsl:with-param name="Count">
<xsl:value-of select="$Count + 1"/>
</xsl:with-param>
</xsl:call-template>
</xsl:otherwise>
</xsl:choose>
</xsl:template>

Answer 3

You can try something like this. You can use a replace instead of 'substring-before' and 'after' if this function is supported.
<xsl:template match="SynchError">
<xsl:apply-templates select="ErrorParameter[1]">
<xsl:with-param name="text"><xsl:value-of select="ErrorText"/></xsl:with-param>
<xsl:with-param name="position">1</xsl:with-param>
</xsl:apply-templates>
</xsl:template>
<xsl:template match="ErrorParameter">
<xsl:param name="text"/>
<xsl:param name="position"/>
<xsl:apply-templates select="following::ErrorParameter">
<xsl:with-param name="position"><xsl:value-of select="number($position)+1"/></xsl:with-param>
<xsl:with-param name="text"><xsl:value-of select="concat(substring-before($text,concat('%',$position)),ErrorParameterValue,substring-after($text,concat('%',$position)))"/></xsl:with-param>
</xsl:apply-templates>
<xsl:if test="not(following::ErrorParameter)">
<xsl:value-of select="concat(substring-before($text,concat('%',$position)),ErrorParameterValue,substring-after($text,concat('%',$position)))"/>
</xsl:if>
</xsl:template>
</xsl:stylesheet>

Answer 4

Here's another way you could look at it:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/">
<output>
<xsl:call-template name="merge">
<xsl:with-param name="string" select="Message/Invalid/InvalidBody/SynchError/ErrorText"/>
<xsl:with-param name="parameters" select="Message/Invalid/InvalidBody/SynchError/ErrorParameter"/>
</xsl:call-template>
</output>
</xsl:template>
<xsl:template name="merge">
<xsl:param name="string"/>
<xsl:param name="parameters"/>
<xsl:param name="flag" select="'%'"/>
<xsl:choose>
<xsl:when test="contains($string, $flag)">
<xsl:variable name="subsequent-char"
select="substring(translate(substring-after($string, $flag), '0123456789', ''), 1, 1)"/>
<xsl:variable name="i"
select="substring-before(substring-after($string, $flag), $subsequent-char)" />
<xsl:value-of select="substring-before($string, $flag)"/>
<xsl:value-of select="$parameters[number($i)]/ErrorParameterValue"/>
<!-- recursive call -->
<xsl:call-template name="merge">
<xsl:with-param name="string" select="substring-after($string, concat($flag, $i))"/>
<xsl:with-param name="parameters" select="$parameters"/>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$string"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>