testEvaluateAsBooleanNamespaces

[ralph.poellath]

Hi,

AbstractXPathTemplateTestCase. testEvaluateAsBooleanNamespaces() from SWS-1.0.3 evaluates the following expression against the xml in namespaces.xml and asserts the result is true:

/prefix1:root/prefix2:child/prefix2:boolean

<root xmlns="namespace1">
    <prefix:child xmlns:prefix="namespace2">
        <prefix:text>text</prefix:text>
        <prefix:number>42.0</prefix:number>
        <prefix:boolean>1</prefix:boolean>
    </prefix:child>
</root>

This testcase does not fail if I replace the 1 with a 0, or any other non-empty string. Is this the expected behaviour?

Cheers,
-Ralph.

[Arjen Poutsma]

Yes . From the XPath spec: http://www.w3.org/TR/xpath#section-Boolean-Functions:

The boolean function converts its argument to a boolean as follows:

• a number is true if and only if it is neither positive or negative zero nor NaN
• a node-set is true if and only if it is non-empty
• a string is true if and only if its length is non-zero
• an object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type

[ralph.poellath]

Thanks Arjen, I just noticed your reply while writing down my own findings..

Turns out this is the expected behaviour, it's just not very intuitive:

While XPath expressions select nodes in the XML document, the XPath API allows the selected nodes to be coalesced into [...] other data types. [...] When a Boolean return type is requested, Boolean.TRUE is returned if one or more nodes were selected; otherwise, Boolean.FALSE is returned.

I falsely assumed XPath 1.0 would recognize schema datatypes, which it doesn't (XPath 2.0 does, but there seems to be no open source implementation).

Therefore, the literals "true" and "false" in a xs:boolean represent the boolean values True and False according to xml schema, but XPath 1.0 will evaluate both of them to True. The same goes for other datatypes as well: "12.78e-2" is a valid value for xs:double, but evaluates to Double.NaN.

javax.xml.datatype provides converters between schema and java types, but only for date and time related stuff. The package summary mentions the mappings for schema built-in datatypes in JAXB, but I haven't yet figured out how to use those as lightweight converters ("evaluate this string as xs:boolean") without full un/marshalling.

Maybe that test case really should contain "0" or "false", so people like me won't draw the wrong conclusions..

Cheers,
-Ralph.

[ralph.poellath]

For the archive: XMLBeans contains easy to use converters between java and schema's built-in data types:

Node n = jaxp13XPathTemplate.evaluateAsNode(expression, context);
boolean b = XmlBoolean.Factory.parse(n).getBooleanValue();

This results in b being True for values of "true" or "1", False for values of "false" or "0", and throws an exception otherwise.

Cheers,
-Ralph.