How can I convert scala.xml.Elem to something compatible with the javax.xml APIs?

interop, java, scala, xml

Solution

What you want is possible - you just have to gently tell the Scala compiler how to go from `scala.xml.Elem` to `javax.xml.transform.stream.StreamSource` by declaring an implicit method.

import java.io.StringReader
import javax.xml.transform.stream.StreamSource
import javax.xml.validation.{Schema, SchemaFactory}
import javax.xml.XMLConstants
import scala.xml.Elem

val schemaXml = <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
                  <xsd:element name="foo"/>
                </xsd:schema>
val schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

implicit def toStreamSource(x:Elem) = new StreamSource(new StringReader(x.toString))

// Very possible, possibly still not any good:
val schema = schemaFactory.newSchema(schemaXml)

It isn't any more efficient, but it sure is prettier once you get the implicit method definition out of the way.

Problem

I have a Scala representation of some XML (i.e. a `scala.xml.Elem`), and I'd like to use it with some of the standard Java XML APIs (specifically SchemaFactory). It looks like converting my `Elem` to a `javax.xml.transform.Source` is what I need to do, but I'm not sure. I can see various ways to effectively write out my `Elem` and read it into something compatible with Java, but I'm wondering if there's a more elegant (and hopefully more efficient) approach? Scala code: ``` import java.io.StringReader import javax.xml.transform.stream.StreamSource import javax.xml.validation.{Schema, SchemaFactory} import javax.xml.XMLConstants val schemaXml = <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="foo"/> </xsd:schema> val schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI); // not possible, but what I want: // val schema = schemaFactory.newSchema(schemaXml) // what I'm actually doing at present (ugly) val schema = schemaFactory.newSchema(new StreamSource(new StringReader(schemaXml.toString))) ```

Original source