Java: XSD 1.1 schema validation of XML with asserts

Question

I want to test generated XML files against a XSD 1.1 file containing assertions and I would like to do that in Java.

My XML content is:

<?xml version="1.0" encoding="UTF-8"?>
<Person xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="person.xsd">
  <Name>John Doe</Name>
  <Age>17</Age>
</Person>

The XSD content is as follows and it contains two assertions:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"
           vc:minVersion="1.1">
  <xs:element name="Person">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="Name" type="xs:string"/>
        <xs:element name="Age" type="xs:integer"/>
      </xs:sequence>
      <xs:assert test="Age &gt;= 18"/>
      <xs:assert test="(string-length(Name) > 15)"/>
    </xs:complexType>
  </xs:element>
</xs:schema>

I use:

implementation("org.opengis.cite.xerces:xercesImpl-xsd11:2.12-beta-r1667115")

as dependency in my build.gradle.kts file. And the following Java code works:

// That's the important String which instantiates a xsd 1.1 aware schema factory + validator
SchemaFactory sf = SchemaFactory.newInstance("http://www.w3.org/XML/XMLSchema/v1.1");
Schema s = sf.newSchema(new StreamSource(getClass().getResourceAsStream(xsdFilePath)));
Validator v = s.newValidator();
v.validate(new StreamSource(getClass().getResourceAsStream(xmlFilePath)));

Hooray, now I get a validation exception:

Exception in thread "main" org.xml.sax.SAXParseException; lineNumber: 6; columnNumber: 10; cvc-assertion: Assertion evaluation ('Age >= 18') for element 'Person' on schema type '#AnonType_Person' did not succeed. 

Problem

When I fix that age to 18, then I don't get a validation error regarding the name (length > 15), but I get

Exception in thread "main" java.lang.NoClassDefFoundError: com/ibm/icu/text/UTF16
    at org.eclipse.wst.xml.xpath2.processor.internal.function.FnStringLength.string_length(FnStringLength.java:105)
    at org.eclipse.wst.xml.xpath2.processor.internal.function.FnStringLength.evaluate(FnStringLength.java:74)
    at org.eclipse.wst.xml.xpath2.processor.DefaultDynamicContext.evaluate_function(DefaultDynamicContext.java:194)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1611)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.FunctionCall.accept(FunctionCall.java:46)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:2139)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.FilterExpr.accept(FilterExpr.java:52)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1258)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.XPathExpr.accept(XPathExpr.java:43)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.do_bin_args(DefaultEvaluator.java:803)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:614)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.CmpExpr.accept(CmpExpr.java:106)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.do_expr(DefaultEvaluator.java:315)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1573)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.ParExpr.accept(ParExpr.java:40)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:2139)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.FilterExpr.accept(FilterExpr.java:52)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1258)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.XPathExpr.accept(XPathExpr.java:43)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1607)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.FunctionCall.accept(FunctionCall.java:46)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:2139)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.FilterExpr.accept(FilterExpr.java:52)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:1258)
    at org.eclipse.wst.xml.xpath2.processor.internal.ast.XPathExpr.accept(XPathExpr.java:43)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.do_expr(DefaultEvaluator.java:315)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.visit(DefaultEvaluator.java:336)
    at org.eclipse.wst.xml.xpath2.processor.ast.XPath.accept(XPath.java:43)
    at org.eclipse.wst.xml.xpath2.processor.DefaultEvaluator.evaluate(DefaultEvaluator.java:290)
    at org.apache.xerces.impl.xs.AbstractPsychoPathXPath2Impl.evaluateXPathExpr(Unknown Source)
    at org.apache.xerces.impl.xs.XMLAssertPsychopathXPath2Impl.evaluateOneAssertion(Unknown Source)
    at org.apache.xerces.impl.xs.XMLAssertPsychopathXPath2Impl.evaluateAssertionsFromAComplexType(Unknown Source)
    at org.apache.xerces.impl.xs.XMLAssertPsychopathXPath2Impl.processAllAssertionsOnElement(Unknown Source)
    at org.apache.xerces.impl.xs.XMLAssertPsychopathXPath2Impl.endElement(Unknown Source)
    at org.apache.xerces.impl.xs.XSDAssertionValidator.handleEndElement(Unknown Source)
    at org.apache.xerces.impl.xs.XMLSchemaValidator.assertionValidatorEndElementDelegate(Unknown Source)
    at org.apache.xerces.impl.xs.XMLSchemaValidator.handleEndElement(Unknown Source)
    at org.apache.xerces.impl.xs.XMLSchemaValidator.endElement(Unknown Source)
    at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanEndElement(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
    at org.apache.xerces.jaxp.validation.StreamValidatorHelper.validate(Unknown Source)
    at org.apache.xerces.jaxp.validation.ValidatorImpl.validate(Unknown Source)
    at java.xml/javax.xml.validation.Validator.validate(Validator.java:124)
    at org.example.HelloWorld.validateXMLSchemaXerxes(HelloWorld.java:50)
    at org.example.HelloWorld.main(HelloWorld.java:31)
Caused by: java.lang.ClassNotFoundException: com.ibm.icu.text.UTF16
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
    ... 48 more

Question:

1. How to fix that problem?
2. In 2024, is there still no other open source library available which can validate XSD 1.1 assertions?

Answer 1

1. It's clearly failing because it's expecting ICU4J to be on the classpath, and it can't find it.

2. No, there is no other open source implementation available. (It took me about a year to write the (commercial) schema processor in Saxon-EE, so this isn't exactly surprising.)