How can I get the xml Node type based on schema definition in Java?

Question

Let's say I have a doc.xml and corresponding doc.xsd. I use xpath to retrieve some nodes, so I get a list of org.w3c.dom.Node. How can I get type of each node from schema, eg. xs:integer, xs:string etc ?

Some solution would be to parse schema with xpath query "//NodeName[@type]" using node.getNodeName() as NodeName, but that's not perfect. I can't be sure that schema is elegant - what if NodeName exists in many places in schema and has not been extracted as a separate type?

So generally I am looking for a reliable solution to get the node type for ANY valid xml & xsd.

Answer 1

Unfortunately types as defined in an XML Schema (XSD) or Document Type Definition (DTD) are not directly tied to XML document they validate. The elements and attributes in an XML document do not inherently have a type they are just text. Think of an XSD as a script that validates an XML document rather than a set of type annotations for elements and attributes.

The XML specification does not define types as you are thinking of them here. Even Document Type Definitions (DTD) which can be embedded inside XML documents more about the structure of the document not the type of the data contained in elements and attributes.

The type system described in XML Schema is an optional layer of validation that can be applied to XML documents. Since this validation optional the standard XML APIs do not provide a way to bind the validation rules in an XSD to the actual attributes and elements.

I think it would be possible for an XML API to provide a mechanism to bind an XSD to a specific XML document, but I am not aware of an XML parser that does this. One reason why this is not so easy is that the type system that is defined in XML Schema is much richer than is supported in most mainstream programming languages. In your example you may only be interested in xs:integer, xs:string and the like but in XML Schema you can create types that specify ranges, patterns and other things that are just not possible with data types in most programming languages. To represent this complex type system in Java or any programming language would have to be done through a fairly complex API. The the question becomes it is really worth it? I would say probably not.

Answer 2

You should consider using JAXB. It will create Java classes for you based on the schema type. Then your XML docs are read into those classes, which are typed according to how you defined your XSD. Therefore xsd:int maps to java int(or Integer wrapper class, I can't recall), etc.

Answer 3

Cast your DOM Elements to TypeInfo: from there, you can access the type information you're looking for.