Changing the XML namespace with Scala

Question

I use scala to load an XML file from a file using a method scala.xml.XML.loadFile(). The documents I'm working with have existing namespaces, and I want to change the namespace to another using scala. For example, the document has xmlns " http://foo.com/a " with the prefix "a" - I would like to change the namespace and prefix for the document to http://foo.com/b "and" b "respectively.

It seems easy, and I feel like I'm missing something obvious here. I have no problem getting the namespace from the returned Elemfrom the reference method loadFile().

Answer 1

Here it is. Since NamespaceBinding is nested (each ns has a parent except TopScope), we need to fix it to fix this. In addition, each ns has a URI and a prefix, and we need to change both.

In the function below, only one specific URI and prefix will be changed, and it will check all namespaces to see if the prefix or URI needs to be changed. It will change the prefix or URI independently, which may not be the way it should. However, it is not very important to fix this.

As elsewhere, just pattern matching on Elem to recurs to every part of XML. Oh yes, this also changes the prefix of the elements. Again, if this is not what you need, it’s easy to change.

, "" XML - . , , . XML, . , , - .

def changeNS(el: Elem, 
             oldURI: String, newURI: String, 
             oldPrefix: String, newPrefix: String): Elem = {
  def replace(what: String, before: String, after: String): String =
    if (what == before) after else what

  def fixScope(ns: NamespaceBinding): NamespaceBinding =
    if(ns == TopScope)
      TopScope
    else new NamespaceBinding(replace(ns.prefix, oldPrefix, newPrefix),
                              replace(ns.uri, oldURI, newURI),
                              fixScope(ns.parent))

  def fixSeq(ns: Seq[Node]): Seq[Node] = for(node <- ns) yield node match {
    case Elem(prefix, label, attribs, scope, children @ _*) => 
      Elem(replace(prefix, oldPrefix, newPrefix), 
           label, 
           attribs, 
           fixScope(scope), 
           fixSeq(children) : _*)
    case other => other
  }
  fixSeq(el.theSeq)(0).asInstanceOf[Elem]
}

. . , NamespaceBinding equals, . , 2138, , Scala 2.8 .

, . . NamespaceBinding .

  def changeNS(el: Elem, 
             oldURI: String, newURI: String, 
             oldPrefix: String, newPrefix: String): Elem = {
  val namespaces = scala.collection.mutable.Map.empty[List[(String, String)],NamespaceBinding]

  def replace(what: String, before: String, after: String): String =
    if (what == before) after else what

  def unfoldNS(ns: NamespaceBinding): List[(String, String)] = ns match {
    case TopScope => Nil
    case _ => (ns.prefix, ns.uri) :: unfoldNS(ns.parent)
    }

  def foldNS(unfoldedNS: List[(String, String)]): NamespaceBinding = unfoldedNS match {
    case knownNS if namespaces.isDefinedAt(knownNS) => namespaces(knownNS)
    case (prefix, uri) :: tail =>
      val newNS = new NamespaceBinding(prefix, uri, foldNS(tail))
      namespaces(unfoldedNS) = newNS
      newNS
    case Nil => TopScope
  }

  def fixScope(ns: NamespaceBinding): NamespaceBinding =
    if(ns == TopScope)
      ns
    else {
      val unfoldedNS = unfoldNS(ns)
      val fixedNS = for((prefix, uri) <- unfoldedNS) 
                    yield (replace(prefix, oldPrefix, newPrefix), replace(uri, oldURI, newURI))

      if(!namespaces.isDefinedAt(unfoldedNS))
        namespaces(unfoldedNS) = ns  // Save for future use

      if(fixedNS == unfoldedNS)
        ns
      else 
        foldNS(fixedNS)
    }

  def fixSeq(ns: Seq[Node]): Seq[Node] = for(node <- ns) yield node match {
    case Elem(prefix, label, attribs, scope, children @ _*) => 
      Elem(replace(prefix, oldPrefix, newPrefix), 
           label, 
           attribs, 
           fixScope(scope), 
           fixSeq(children) : _*)
    case other => other
  }
  fixSeq(el.theSeq)(0).asInstanceOf[Elem]
}

Answer 2

. . .