How do I check for the existence of an external file with XSL?

Question

I've found a lot of examples that reference Java and C for this, but how do I, or can I, check for the existence of an external file with XSL.

First, I realize that this is only a snippet, but it's part of a huge stylesheet, so I'm hoping it's enough to show my issue.

    <!-- Use this template for Received SMSs -->
<xsl:template name="ReceivedSMS">
    <!-- Set/Declare "SMSname" variable (local, evaluates per instance) -->
    <xsl:variable name="SMSname">
        <xsl:value-of select=" following-sibling::Name"/>
    </xsl:variable>
    <fo:table font-family="Arial Unicode MS" font-size="8pt" text-align="start">
        <fo:table-column column-width=".75in"/>
        <fo:table-column column-width="6.75in"/>
        <fo:table-body>
            <fo:table-row>
                <!-- Cell contains "speakers" icon -->
                <fo:table-cell display-align="after">
                    <fo:block text-align="start">
                        <fo:external-graphic src="../images/{$SMSname}.jpg" content-height="0.6in"/>

What I'd like to do, is put in an "if" statement, surronding the {$SMSname}.jpg line. That is:

                     <fo:block text-align="start">
                        <xsl:if test="exists( the external file {$SMSname}.jpg)">
                            <fo:external-graphic src="../images/{$SMSname}.jpg" content-height="0.6in"/>                            
                        </xsl:if>
                        <xsl:if test="not(exists( the external file {$SMSname}.jpg))">
                            <fo:external-graphic src="../images/unknown.jpg" content-height="0.6in"/>                            
                        </xsl:if>
                    </fo:block>                       

Because of "grouping", etc., I'm using XSLT 2.0. I hope that this is something that can be done. I hope even more that it's something simple.

As always, thanks in advance for any help. LO

Answer 1

For anyone else who might stumble upon this old question, by piecing together information from various sources on the internet, I came up with this XSLT2 function that uses a Java extension for checking whether a file exists:

<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:java="http://www.java.com/"
  exclude-result-prefixes="java xs">

  <xsl:function name="java:file-exists" xmlns:file="java.io.File" as="xs:boolean">
    <xsl:param name="file" as="xs:string"/>
    <xsl:param name="base-uri" as="xs:string"/>

    <xsl:variable name="absolute-uri" select="resolve-uri($file, $base-uri)" as="xs:anyURI"/>
    <xsl:sequence select="file:exists(file:new($absolute-uri))"/>
  </xsl:function>

</xsl:stylesheet>

You can then use the function like this:

<xsl:if test="java:file-exists($filename, base-uri())">
  <!-- ... -->
</xsl:if>

This works at least with Saxon 9.1.0.5J — haven't tested it with any other XSLT processors.

Note: If the file for whose existence you're checking is an XML file and you're using XSLT2, you can also use the built-in doc-available() function:

<xsl:if test="doc-available('hello_world.xml')">
  <!-- ... -->
</xsl:if>