Find items that can be repeated in an xml schema using Java

Question

I want to deduce from an XML schema the couple (parentTag, childTag) such that it is allowed for parentTag to contain multiple instances of childTag as direct children.

Doing that by hand, I look for the maxOccurs attribute in the schema, look the element tag, and tag of the direct parent.

For example, from

<xs:complexType name="aType">
     <xs:sequence>
          <xs:element ref="B" maxOccurs="unbounded"/>
     </xs:sequence>
</xs:complexType>

<xs:element name="A" type="aType">
<xs:element name="ANOTHER" type="aType">

I should obtain the couples (A,B) and (ANOTHER,B).

I have a working solution using XSLT to convert my schema to a list of such (parentTag, childTag) couples.

Is there an elegant way to do this in Java ? Which library would you recommend to implement this ?

Answer 1

To process XML schemas in Java (without XSLT), we use Xerces2 Java Parser: http://xerces.apache.org/xerces2-j/

The following packages/classes may be needed:

import org.w3c.dom.*;
import org.apache.xerces.xs.*;
import org.apache.xerces.dom.DOMXSImplementationSourceImpl;
import org.apache.xerces.impl.xs.util.StringListImpl;
import org.apache.xerces.util.XMLCatalogResolver;

Then, the processing of an XSD file goes like this:

// Obtain the XML Schema implementation
XSImplementation impl = (XSImplementation)
  (new DOMXSImplementationSourceImpl()).getDOMImplementation(XMLConstants.XSD_LOADER_NAME);

// Get schema loader
XSLoader schemaLoader = impl.createXSLoader (null);

// Optional. Specify error handler
DOMErrorHandler errorHandler = ....;
DOMConfiguration config = schemaLoader.getConfig();
config.setParameter("error-handler", errorHandler);

// Optional. Specify XML catalog resolver.
// This may be needed to redirect internal DTD/schema file references
XMLCatalogResolver catalogResolver = ...;
config.setParameter("resource-resolver", catalogResolver);

String xsdURI = ...; // the location of schema file

// read schema
XSModel xsModel = schemaLoader.loadURI(xsdURI);

// PROCESS SCHEMA (here, you can do anything you want)

XSNamedMap xsMap;

// process top-level element declarations
xsMap = xsModel.getComponents(XSConstants.ELEMENT_DECLARATION);
for (int i = 0; i < xsMap.getLength(); i ++)
{
  XSElementDeclaration xsElementDecl = (XSElementDeclaration) xsMap.item(i);
  ...
}

// process top-level type definitions
xsMap = xsModel.getComponents(XSConstants.TYPE_DEFINITION);
for (int i = 0; i < xsMap.getLength(); i ++)
{
  XSTypeDefinition xsTDef = (XSTypeDefinition) xsMap.item(i);
  ...
}

// process model group definitions
xsMap = xsModel.getComponents(XSConstants.MODEL_GROUP_DEFINITION);
for (int i = 0; i < xsMap.getLength(); i ++)
{
  XSModelGroupDefinition xsGroupDef = (XSModelGroupDefinition) xsMap.item(i);
  ...
}

...