XPathAPI with SVGDocument

[Krzysztof Jurkowski]

Hi,
I want to create a find tool for my JSVGCanvas, so that user can zoom on a certain text in the drawing.
The svg file looks as follows:

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN"
    "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd" >
<svg>
    <!--Generated by the Batik Graphics2D SVG Generator-->
    <defs id="genericDefs"/>
    <g>
        <g font-family="'Arial'">
            <line y2="33896" fill="none" x1="47630" x2="50108" y1="33343"/>
            <rect fill="white" x="50150" width="9" height="14" y="33021" stroke="none"/>
            <rect fill="none" x="50150" width="9" height="14" y="33021"/>
            <text x="50152" xml:space="preserve" y="33033" stroke="none">1</text>
            <line y2="33035" fill="none" x1="47630" x2="50150" y1="33343"/>
            <line y2="34325" fill="none" x1="50108" x2="52589" y1="33896"/>
            <line y2="34126" fill="none" x1="52625" x2="55119" y1="33834"/>
            <rect fill="white" x="55136" width="18" height="15" y="33835" stroke="none"/>
            <rect fill="none" x="55136" width="18" height="15" y="33835"/>
            <text x="55138" xml:space="preserve" y="33848" stroke="none">65</text>
            <line y2="33850" fill="none" x1="52625" x2="55136" y1="33834"/>
            <rect fill="white" x="55119" width="25" height="15" y="34111" stroke="none"/>
            <rect fill="none" x="55119" width="25" height="15" y="34111"/>
            <text x="55121" xml:space="preserve" y="34124" stroke="none">238</text>
            <rect fill="white" x="52625" width="18" height="15" y="33819" stroke="none"/>
            <rect fill="none" x="52625" width="18" height="15" y="33819"/>
            <text x="52627" xml:space="preserve" y="33832" stroke="none">65</text>
            etc...

To do it I just need to select a text node in the SVGDocument, get the x and y attributes and I have the coordinates or the node on the drawing.

The problem is that when I call:

XPathAPI.selectNodeList(svgDocument.getDocumentElement(), "//text[.=\"" + value + "\"]");

than the returned list is empty.

Same story with:

XPathAPI.selectSingleNode(svgDocument.getDocumentElement(), "//text[.=\"" + value + "\"]");

it returns null!

I tested this XPath expression with http://ponderer.org/download/xpath/ and it works fine.
What am I doing wrong?

[Paul Clapham]

Unfortunately for us, you haven't posted an XPath expression. What you posted was some Java code which produces an XPath expression. It would be much easier if you posted the actual XPath expression which you say you tested. (Presumably that site just tests expressions for well-formedness.)

[Krzysztof Jurkowski]

Paul Clapham wrote:Presumably that site just tests expressions for well-formedness.

Actually it highlights expression matching nodes, so I'm sure it should return a result.

I tried: //text[.="11"] and //text[.='11'].
None works.

Even when I try //text, which should return all the text nodes it gives me an empty list.

On the other hand I tried to execute equivalent code in JDom:

DOMBuilder domBuilder = new DOMBuilder();
Document jdomDocument = domBuilder.build(svgDocument);
List textList = XPath.selectNodes(jdomDocument, "//text");

and it also returns an empty list.
So something must be wrong with the svg document or the XPath expression.
If you wish you can download a sample document from:
http://dl.getdropbox.com/u/296382/tree.svg

[Paul Clapham]

Here's what I think the problem is: that DTD referenced at the beginning applies a default attribute to your <svg> root element. And that attribute looks like this:

xmlns="http://www.w3.org/2000/svg"

So, that declares a default namespace for the document and all of the elements are in that namespace. Your XPath expression is looking for <text> elements which are in no namespace but there aren't any. All of the <text> elements are in the "http://www.w3.org/2000/svg" namespace.

You can fix this by searching for <text> elements which are in the "http://www.w3.org/2000/svg" namespace. Attach a namespace binding to that XPath expression which has prefix "svg" and namespace URI "http://www.w3.org/2000/svg". (I don't know how to do that but there must be a way.) Then change the XPath expression to search for <svg:text> elements.

[Krzysztof Jurkowski]

You're right - this was a problem of default namespace.
I found a working solution for JDOM:

DOMBuilder domBuilder = new DOMBuilder();
Document jdomDocument = domBuilder.build(svgDocument);
XPath xpath = XPath.newInstance("//svg:text");
xpath.addNamespace("svg", svgDocument.getRootElement().getNamespaceURI());
List result = xpath.selectNodes(jdomDocument);

But I cannot figure out how to do it with XPathAPI... I tried:

NodeList result = XPathAPI.selectNodeList(svgDocument.getDocumentElement(), "//svg:text", svgDocument.getRootElement());

but it throws: com.sun.org.apache.xpath.internal.domapi.XPathStylesheetDOM3Exception: Prefix must resolve to a namespace: svg

Do you know what is wrong with the XPathAPI code? Or perhaps could you suggest an alternative for XPathAPI that accepts org.w3c.dom.Document.

Thanks!

[Paul Clapham]

Your document uses the default namespace. But you need a prefix for the namespace so that XPath knows to search for elements with a particular namespace URI. So my quick look at the XPathAPI documentation (that is the Xalan XPathAPI, right?) suggests you're going to have to provide a PrefixResolver to the API because of that.

And there's only one method in there which takes a PrefixResolver as a parameter, so I guess you will have to make do with that.