This post explains how to use XML Schema to validate your document and XInclude to partition it in manageable chunks in Java using Xerces.

For this example I use the following documents:

• main.xml the main document, imports include.xml
• include.xml the included document, contains just a single element
• main.xsd a simple schema for the main document

main.xml
<?xml version="1.0"?>
<root xmlns="http://main.xml"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      xsi:schemaLocation="http://main.xml
      file:///<i>path to schema</i>/main.xsd">

  <e id="1"/>
  <e id="2"/>
  <e id="3"/>
  <b><xi:include href="include.xml"/></b>
  <e id="4"/>
  <e id="5"/>
  <e id="6"/>
</root>

And this is the included file:

include.xml
<?xml version="1.0"?>
<e xmlns="http://main.xml" id="23"/>

and a very simple Schema to validate the file:

main.xsd
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema targetNamespace="http://main.xml"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:sn="http://main.xml"
  elementFormDefault="qualified">

  <xsd:element name="root">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="e" type="sn:elementType" maxOccurs="unbounded"/>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <xsd:complexType name="elementType">
    <xsd:attribute name="id" type="xsd:string" use="required"/>
  </xsd:complexType>
</xsd:schema>

The solution seems obvious, use a SAXParser and set the features for Schema Validation and XInclude to true.

final SAXBuilder saxB = new SAXBuilder("org.apache.xerces.parsers.SAXParser", true);
saxB.setFeature("http://apache.org/xml/features/validation/schema", true);
saxB.setFeature("http://apache.org/xml/features/xinclude", true);
saxB.build("main.xml");

Sadly, it fails with Exception in thread "main" org.jdom.JDOMException: Error on line 12 of document a pathmain.xml: Error attempting to parse XML file (href='include.xml'). Line 12 is the line containing the XInclude statement which suggested an error in the syntax. But multiple rereads of the spec didn’t help so turned off Schema Validation for a change. Now everything worked fine and a look at the document shows what went wrong with the Schema Validation:

<?xml version="1.0" encoding="UTF-8"?>
<root xmlns="http://main.xml"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:xi="http://www.w3.org/2001/XInclude"
      xsi:schemaLocation="http://main.xml
      file:///<i>path to schema</i>/test.xsd">

  <e id="1" />
  <e id="2" />
  <e id="3" />
  <e id="23" <b>xml:base="include.xml" </b>/>
  <e id="4" />
  <e id="5" />
  <e id="6" />
</root>

Xerces inserts a xml:base attribute when in insert an element and this attribute is not allowed in my Schema. But fortunately I don’t have to change my schema to suit this. There’s a feature called fixup-base-uris (http://apache.org/xml/features/xinclude/fixup-base-uris) which removes these additional attributes.

final SAXBuilder saxB = new SAXBuilder("org.apache.xerces.parsers.SAXParser", true);
saxB.setFeature("http://apache.org/xml/features/validation/schema", true);
saxB.setFeature("http://apache.org/xml/features/xinclude", true);
saxB.setFeature("http://apache.org/xml/features/xinclude/fixup-base-uris", false);

This works fine, with one minor problem left: if there is an error in the included XML document, it fails with Exception in thread "main" org.jdom.JDOMException: Error on line 12 of document file:a path/main.xml: Error attempting to parse XML file (href='include.xml'). which is not very helpful. I’ll post a workaround for this problem tomorrow.