Saxon: Cannot call static method expecting String with xs:string parameter from XSLT

Question

I am trying to call a static Java method from my XSLT stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                              xmlns:digest="java:org.apache.commons.codec.digest.DigestUtils">
<xsl:output method="xml" encoding="utf-8" indent="yes"/>

<xsl:template match="user">
  <user>
    <firstname>
      <xsl:value-of select="value[@type='firstname'][1]" />
    </firstname>
    <lastname>
      <xsl:value-of select="value[@type='name'][1]" />
    </lastname>
    <password>
      <xsl:variable name="password" select="string(value[@type='password'][1])" />
      <xsl:value-of select="digest:md5Hex($password)"
                    disable-output-escaping="yes" />
    </password>
  </user>
</xsl:template>

The DigestUtils class is found and the static md5Hex-method [1] as well. The problem is, that there are three possible ways to invoke the method, namely with a byte[], an InputStream or a String. Given that the "password" variable is of type xs:string, I assumed that Saxon would automatically choose the last option. But instead, it insists on the byte[]-method and fails accordingly:

[...]
Loading org.apache.commons.codec.digest.DigestUtils
Looking for method md5Hex in Java class class org.apache.commons.codec.digest.DigestUtils
Number of actual arguments = 1
[...]
Trying method md5Hex: name matches
Method is static
Method has 1 argument; expecting 1
Found a candidate method:
    public static java.lang.String org.apache.commons.codec.digest.DigestUtils.md5Hex(byte[])
Trying method md5Hex: name matches
Method is static
Method has 1 argument; expecting 1
Found a candidate method:
    public static java.lang.String org.apache.commons.codec.digest.DigestUtils.md5Hex(java.io.InputStream) throws java.io.IOException
Trying method md5Hex: name matches
Method is static
Method has 1 argument; expecting 1
Found a candidate method:
    public static java.lang.String org.apache.commons.codec.digest.DigestUtils.md5Hex(java.lang.String)
[...]
Finding best fit method for arguments
Trying option 0: public static java.lang.String org.apache.commons.codec.digest.DigestUtils.md5Hex(byte[])
Conversion preferences are [24]
Trying option 1: public static java.lang.String    org.apache.commons.codec.digest.DigestUtils.md5Hex(java.io.InputStream) throws java.io.IOException
Conversion preferences are [80]
Trying option 2: public static java.lang.String org.apache.commons.codec.digest.DigestUtils.md5Hex(java.lang.String)
Conversion preferences are [80]
Eliminating option 1
Eliminating option 2
Number of candidate methods remaining: 1
Error at xsl:template on line 14 column 30 of migrate_users.xsl:
  Cannot convert from xs:string to byte
Failed to compile stylesheet. 1 error detected.

Is there a way to force Saxon to use the String-method?

[1] http://commons.apache.org/codec/api-release/org/apache/commons/codec/digest/DigestUtils.html#md5Hex(java.lang.String)

-- update: A colleague just found the company's license key for Saxon 9.4PE. Unfortunately the error persists, the only thing that changed was that the conversion preference for the byte[]-method went from 24 to 31.

Barnaby Shearer · Accepted Answer · 2012-07-12 09:22:47Z

4

You need to type your variable:

<xsl:variable as="xs:string" name="password" select="string(value[@type='password'][1])" />

or cast it in the call:

<xsl:value-of select="digest:md5Hex(xs:string($password))"
                disable-output-escaping="yes" />

With the xs namespace defined as:

xmlns:xs="http://www.w3.org/2001/XMLSchema"

answered Jul 12, 2012 at 9:22

Barnaby Shearer

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1 Comment

jbaiter Over a year ago

Thank you, casting the variable during the call did the trick. Typing the variable didn't help, though. Anyhow, the question remains why it didn't work in the first place, as Saxon clearly received an xs:string argument (as can be seen from the error message).

Michael Kay · Accepted Answer · 2012-07-12 10:32:33Z

Saxon tries to decide which method to use at compile time, based on its static analysis of the type of the supplied argument. If the inferred static type allows a sequence (as distinct from a singleton), then a method that expects an array or collection will always win over a method that expects a singleton: so the fact that the method expecting byte[] was preferred means that Saxon wasn't able to work out that the supplied value was a singleton. Clearly the cast to string is enough to enable this inference.

It's disappointing that adding type information to the variable declaration isn't enough. The reason for this is that the decision on which method to use is made too early during the compilation process, before the type information has been propagated from the variable declaration to the variable reference. I will look at the possibility of improving this for a future release.

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