XPath 1.0 String Evaluation

The embedded XPath DSL provides a very flexible and performant way to query xml. However, being an embedded DSL, it has the negative of being wed to the compilation cycle. For those seeking a more direct XPath string parsing based experience Scales provides access via the Jaxen project.

The scales-jaxen project is a sub project and must be included separately as a library dependency.

How To Use

The following dependency must be used (instead of scales-xml):

  "scales" %% "scales-jaxen" % "0.3" // or 0.4 for a Scalaz 6.0.4 dependency

After importing the package use the ScalesXPath constructor with either a map of prefix to uri, or a list of PrefixedNamespaces (similar to Elem construction):

  import scales.xml.jaxen._

  // prefix mappings are needed for context
  val aPath = ScalesXPath("//*[1]", Map("pre" -> "urn:prefix"))
  // the type annotation is for illustrative reasons only :->
  val result : Iterable[Either[AttributePath, XmlPath]] = aPath.evaluate(anXmlPath)

  // direct XPath results use get
  val anotherPath = ScalesXPath("string(//*[1])", Map("pre" -> "urn:prefix"))
  // This uses casts to retrieve values, it can throw.
  val string = anotherPath.get[String](anXmlPath)

Results are always returned in Document order.

Rather than dealing with an Either for results, when the developer probably knows what type he wants, xmlPaths and attributePaths can be used:

  val ns = Namespace("test:uri")
  val nsa = Namespace("test:uri:attribs")
  val nsp = nsa.prefixed("pre")

  val builder = 
    ns("Elem") /@ (nsa("pre", "attr1") -> "val1",
      	    	   "attr2" -> "val2",
		   nsp("attr3") -> "val3") /(
      ns("Child"),
      "Mixed Content",
      ns("Child2") /( ns("Subchild") ~> "text" )
    )

  val elems = ScalesXPath("//*")
  elems.xmlPaths(path).map(qname(_)) // List(Elem, Child, Child2, Subchild)
  elems.attributePaths(path).map(qname(_)) // List()

  val attribs = ScalesXPath("//@*")
  attribs.xmlPaths(path).map(qname(_)) // List()
  attribs.attributePaths(path).map(qname(_)) // List(pre:attr3, attr2, pre:attr1)

As a shortcut to ignore namespaces (instead of using prefixes) use:

  ScalesXPath("/html/body/p[2]/table[2]/tr/td/table/tr/td[1]/a/font").withNameConversion(ScalesXPath.localOnly)

The function passed to withNameConversion is of type:

QName => QName

allowing further mappings as needed.

Other Jaxen Tricks

Jaxen provides various extensions to straight forward querying, including adding java extension functions. If possible, of course, use the embedded DSL, if not ScalesXPath is a Jaxen XPath implementation, allowing calls to setFunctionContext, variableContext etc.