Any XSL experts?

Thread view:

Mark Space - 24 Oct 2007 03:21 GMT

Here's a problem that's driving me nuts.

The program below executes correctly as is. There's one line in the xsl
string commented out. If you uncomment that line, the output changes.
It adds the line "I can't jump." That's the value of the <jump> tag.
But I don't ask for this tag to be put in the output anywhere in the xsl
file, so I don't understand why it's appearing in the output.

Can anyone shed some illumination on this conundrum?

package xslweirdness;

import java.io.StringReader;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

public class Main {

private final static String xml = "<?xml version=\"1.0\"?>\n"
+" <monkey>\n"
+" <boy can=\"no\">\n"
+" <jump>I can't jump.</jump>\n"
+" </boy>\n"
+" </monkey>";
private final static String xsl = "<xsl:stylesheet "
+"xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\" "
+"version=\"1.0\">\n"
+" <xsl:output method=\"html\"/>"
+" <xsl:template match=\"/monkey\" >\n"
+" Jumping: <xsl:value-of select=\"boy/@can\" />\n"
// +" <xsl:apply-templates/>"
+" </xsl:template>\n"
+"</xsl:stylesheet>";

public static void main(String[] args) throws Exception {
System.out.println( "XML:--------------------\n" + xml );
System.out.println( "XSL:--------------------\n" + xsl );

StreamSource xslSrc = new StreamSource( new StringReader(xsl) );
TransformerFactory tf = TransformerFactory.newInstance();
Transformer xfrm = tf.newTransformer(xslSrc);
StreamResult stmOut = new StreamResult( System.out );
StreamSource xmlSrc = new StreamSource( new StringReader(xml) );

System.out.println( "transform:--------------------\n" );
xfrm.transform(xmlSrc, stmOut);
}
}

Reply to this Message

Arne Vajhøj - 24 Oct 2007 03:49 GMT

> Here's a problem that's driving me nuts.
>
[quoted text clipped - 5 lines]
>
> Can anyone shed some illumination on this conundrum?

> private final static String xml = "<?xml version=\"1.0\"?>\n"
> +" <monkey>\n"
[quoted text clipped - 11 lines]
> +" </xsl:template>\n"
> +"</xsl:stylesheet>";

That line tells the XSLT processor to process stuff inside what
you have found.

There are the element text inside.

And apperently there are a default template that displays.

I guess you don't want that line !

Arne

Reply to this Message

Mark Space - 24 Oct 2007 06:33 GMT

> There are the element text inside.
>
> And apperently there are a default template that displays.

Yeah that's a good way of thinking about it. There's a default element
that says to just print all values. Weird, I think, but I guess that's
how it works. Thanks!

Reply to this Message

Andrew Thompson - 24 Oct 2007 03:59 GMT

Sub: Any XSL experts?

I probably should not answer this, since I do not
consider myself an 'expert' on anything.

OTOH - I'll make a WAG.*

<http://www.w3schools.com/xsl/xsl_apply_templates.asp>
"The <xsl:apply-templates> element applies a template
to the current element *or to the current element's child
nodes.*"

My use of *bold*.

If that line is changed to ..
+" <xsl:apply-templates select='boy'/>"
..the "I can't jump." line is printed, if changed to..
+" <xsl:apply-templates select='monkey'/>"
..it is not.

* My WAG is - that line prints because you 'told it to'.

Signature

Andrew Thompson
http://www.athompson.info/andrew/

Reply to this Message

Mark Space - 24 Oct 2007 06:37 GMT

> <http://www.w3schools.com/xsl/xsl_apply_templates.asp>
> "The <xsl:apply-templates> element applies a template
[quoted text clipped - 10 lines]
>
> * My WAG is - that line prints because you 'told it to'.

As Arne said, there appears to be a default element. In a "real" xsl
file there are a lot more xsl:templates. I assumed those would be
matched. The presence of a "default" template really kinda fouls things
up, imo. I appreciate that you pointed out that the select command
could be used to modify this behavior, that's probably just what I need.
I'm still trying to wrap my head around how the parse "sees" the
transform.

Thanks for the info!

Reply to this Message

Mike Schilling - 24 Oct 2007 06:26 GMT

> Here's a problem that's driving me nuts.
>
[quoted text clipped - 4 lines]
> anywhere in the xsl file, so I don't understand why it's appearing in
> the output.

<apply-templates> means to process all child nodes. The default action for
a text node, which you haven't overridden, is to output the text.

Reply to this Message

Mark Space - 24 Oct 2007 10:00 GMT

> <apply-templates> means to process all child nodes. The default action for
> a text node, which you haven't overridden, is to output the text.

That makes more sense: because no action was specified, a default one
was supplied. Thanks!

I'm still trying to wrap my head around how the processing actually
occurs. Since this is just basically a fun project, it doesn't matter
if I can ultimately get everything working just perfect. That's good,
because the more I look at the actual input file, the more it appears it
was not designed with any kind of XSL in mind.

Reply to this Message

Pavel Lepin - 24 Oct 2007 12:57 GMT

Follow-ups set to comp.text.xml.

Mark Space <markspace@sbc.global.net> wrote in
<ZQDTi.235$Nz7.5@nlpi070.nbdc.sbc.com>:

>> <apply-templates> means to process all child nodes. The
>> default action for a text node, which you haven't
>> overridden, is to output the text.

The meaning of xsl:apply-templates without select attribute
is described in detail in XSLT 1.0 spec, 5.4. Built-in
template rules are described in 5.8.

> I'm still trying to wrap my head around how the processing
> actually occurs.

Unless I've mistaken the intent of your question, here's the
gist of how XSLT processing works:

An XSLT stylesheet is a set of templates describing how to
construct result tree fragments, using literal result
elements, xsl:element, xsl:attribute, xsl:value-of etc.
Those templates are applied to various node lists.

Of particular interest is xsl:apply-templates and similar
constructs (xsl:apply-imports, xsl:for-each). Those
construct a resulting tree fragment by selecting a nodeset
(by evaluating an XPath expression in select attribute if
specified, or as described in 5.4 otherwise), using it as
current node list and applying templates to it.

The template chosen for every node or attribute in a node
list depends on a set of hairy rules described in 5.5,
involving stuff like 'import precedence', template
specificity, priority attributes on corresponding
xsl:template elements, mode attribute of
xsl:apply-templates, and the particular instruction invoked
to apply templates, but most of that is of little interest
unless/until you run into problems with it.

To start the transformation, an XSLT processor selects the
document node (/) as a current node list and applies
templates to it. The process continues recursively until a
template is reached that constructs a resulting tree
fragment without applying templates to anything else.

How does that work with your sample document and stylesheet:

1. Current node list: document node (/).
Template applied (built-in):

<xsl:template match="*|/">
<xsl:apply-templates/>
</xsl:template>

2. Current node list: root element 'monkey'.
Template applied:

<xsl:template match="/monkey">
Jumping: <xsl:value-of select="boy/@can"/>
<xsl:apply-templates/>
</xsl:template>

3. Current node list: element 'boy'.
Template applied (built-in):

<xsl:template match="*|/">
<xsl:apply-templates/>
</xsl:template>

4. Current node list: element 'jump'.
Template applied (built-in):

<xsl:template match="*|/">
<xsl:apply-templates/>
</xsl:template>

5. Current node list: text node 'I can't jump'.
Template applied (built-in):

<xsl:template match="text()|@*">
<xsl:value-of select="."/>
</xsl:template>

The RTF for 5 therefore is:

I can't jump.

For 4 and 3:

I can't jump.

For 2:

Jumping: no
I can't jump.

For 1:

Jumping: no
I can't jump.

> That's good, because the more I look at the actual input
> file, the more it appears it was not designed with any
> kind of XSL in mind.

I fail to see what leads you to this conclusion.

Oh, and:

Andrew Thompson <u32984@uwe> wrote in <7a264236381b4@uwe>:

> <http://www.w3schools.com/xsl/xsl_apply_templates.asp>
> "The <xsl:apply-templates> element applies a template
> to the current element *or to the current element's child
> nodes.*"

Just goes to show you how little clue those guys at
w3schools have. Not the first time they've been caught at
blatant lies, either.

Signature

It is rare to find learned men who are clean, do not stink,
and have a sense of humour. -- Liselotte in a letter to
Sophie, 30 Jul 1705

Reply to this Message

Any XSL experts?

Free Magazines