Performing complicated XPath queries in Scala

问题

What's the simplest API to use in scala to perform the following XPath queries on a document?

//s:Annotation[@type='attitude']/s:Content/s:Parameter[@role='type' and not(text())]

//s:Annotation[s:Content/s:Parameter[@role='id' and not(text())]]/@type

(s is defined as a nickname for a particular namespace)

The only documentation I can find on Scala's XML libraries has no information on performing complicated real XPath queries.

I used to like JDOM for this purpose (in Java), but since JDOM doesn't support generics, it will be painful to work with in Scala. (Other XML libraries for Java have tended to be even more painful in Java, but I admit I don't know the landscape real well.)

回答1:

//s:Annotation[@type='attitude']/s:Content/s:Parameter[@role='type' and not(text())]

Well, I don't understand the s: notation, and couldn't find it on XPath spec either. However, ignoring that this would look like this:

(
  (xml 
    \\ "Annotation" 
    filter (_ \ "@type" contains Text("x"))
  ) 
  \ "Content" 
  \ "Parameter" 
  filter (el => (el \ "@type" contains Text("type")) && el.isInstanceOf[Text])
)

Note the necessity of parenthesis because of higher precedence of \ over filter. I have changed the formatting to a multi-line expression as the Scala equivalent is just way too verbose for a single line.

I can't answer about namespaces, though. No clue how to work with them on searches, if it's even possible. The docs mention @{uri}attribute for prefixed attributes, not does not mention anything about prefixed elements. Also, note that you need to pass an uri which resolves to the namespace you want, as literal namespaces in search are not supported.

回答2:

I think I'm going to go with lightly pimping XOM. It's a bit of a shame the XOM authors decided against exposing collections of child nodes and the like, but they had more work and less advantage to doing so in Java than in Scala. (And it is an otherwise well-designed library.)

EDIT: I wound up pimping JDOM after all, because XOM doesn't compile XPath queries ahead of time. Since most of my effort was directed towards XPath this time, I was able to come up with a good model that sidesteps most of the generics issues. It shouldn't be too hard to come up with reasonable genericized versions of the methods getChildren and getAttributes and getAdditionalNamespaces in org.jdom.Element (by pimping the library with new methods that have slightly changed names.) I don't think there's a fix for getContent, and I'm not sure about getDescendants.

回答3:

Scales Xml adds both string based full XPath evaluation and an internal DSL providing a fairly complete coverage for querying

回答4:

I guess when scalaxmljaxen is mature, we'll be able to do this reliably on scala's built-in XML classes.

回答5:

I would suggest using kantan.xpath:

 import kantan.xpath._
 import kantan.xpath.implicits._

 input.evalXPath[List[String]](xp"/annotation[@type='attitude']/content/parameter[@role='type' and not(text())]/@value")

This yields:

res1: kantan.xpath.XPathResult[List[String]] = Success(List(foobar))

来源：https://stackoverflow.com/questions/3056337/performing-complicated-xpath-queries-in-scala

标签

java

xml

scala

xpath

jdom