XPath: Node value exists

[Scott Selikoff]

Given an XML such as the following

<data>
<widget>123</widget>
</data>

How would I write an XPath query to determine whether there was a widget with value 123? I know how to write it to find instances of "<widget>" and parse the results in Java, but I was hoping to do it in a single XPath line.

[Matthew Brown]

Something like

/data/widget[. = '123']

[Scott Selikoff]

Ah, I was trying "/data/widget[123]", thanks!

[David Newton]

Or /data/[widget='123'] should work, IIRC.

[ben oliver]

what if we want to say "widget=123 or 234" ?

should it be /data/[widget='123' || widget='234'] ?

[Paul Clapham]

No. The way to say "or" in XPath is "or".

[ben oliver]

Paul Clapham wrote:No. The way to say "or" in XPath is "or".

But I tested

String eval = "/data/[widget='123']";
com.sun.org.apache.xpath.internal.XPathAPI.eval(doc, eval);

it gave me exception as

javax.xml.transform.TransformerException: A location step was expected following the '/' or '//' token.

where "doc" is a Document. There is no problem with this because I tried other "eval" strings and they worked fine.

[Paul Clapham]

Ah, I see. But that's nothing to do with "or", which doesn't even feature in the problem. It's all to do with the fact that all of the XPath expressions posted so far have had the same problem, namely a predicate which doesn't modify anything. Try this instead:

String eval = "/data[widget='123']"; 

[ben oliver]

Paul Clapham wrote:Ah, I see. But that's nothing to do with "or", which doesn't even feature in the problem. It's all to do with the fact that all of the XPath expressions posted so far have had the same problem, namely a predicate which doesn't modify anything. Try this instead:

String eval = "/data[widget='123']"; 

it gives very strange results.. no exception though.

Basically I want to get some boolean type result showing "is it true that there is a data element whose child element widget (assuming only one child element called widget) has value of "123" ? I don't like the "eval" method which always returns an object. How do you come up with a Xpath and returns a true/false kind result to me ?

[g tsuji]

One way to do it is to make good use of the javax.xml.xpath.XPathConstants to specify the desired return type. Like this (with missing parts and variables following the documentation)

String expression="/data[widget='123']";
Boolean b=(Boolean)xpath.evaluate(expression, inputSource, XPathConstants.BOOLEAN);

However, there is too boolean() function, a supported xpath function. Hence, this expression is still a good xpath and it makes the desired result to capture clearer (rather than hidden in the option XPathConstants.BOOLEAN argument).

String expression="boolean(/data[widget='123'])";