Validating xml through xsd files inside a JAR

I try to validate an xml using xsd. So far, everything works fine:

File xsdFile = null;
Source source = new StreamSource(new StringReader(xmlString));
try {
    xsdFile = new ClassPathResource(FacturxConstants.FACTUR_X_MINIMUM_XSD).getFile();
} catch (IOException e) {
    throw new FacturxException(e.getMessage());
}
try {
    SchemaFactory schemaFactory = SchemaFactory
            .newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
    Schema schema = schemaFactory.newSchema(xsdFile);
    Validator validator = schema.newValidator();
    validator.validate(source);
    return true;
} catch (SAXException | IOException e) {
    throw new FacturxException(e.getLocalizedMessage());
}

My issue is the following:
If i compile it in a jar and call the method using the validator, i have errors. As a matter of fact it seems that i can't get the related xsd files.

I tried to solve this issue this way:

Source[] sources = sources = new Source[] {
    new StreamSource(
        new ClassPathResource(FacturxConstants.FACTUR_X_MINIMUM_XSD_QUALIFIED_DATA)
             .getInputStream()),
    new StreamSource(
        new ClassPathResource(FacturxConstants.FACTUR_X_MINIMUM_XSD_REUSABLE)
             .getInputStream()),
     new StreamSource(
        new ClassPathResource(FacturxConstants.FACTUR_X_MINIMUM_XSD_UNQUALIFIED_DATA)
            .getInputStream()),
     new StreamSource(
        new ClassPathResource(FacturxConstants.FACTUR_X_MINIMUM_XSD).getInputStream())

Apparently I do have access to those xsd files but it returns src-resolve: Cannot resolve the name 'udt:IDType' to a(n) 'type definition' component. If i change xsd files order, errors differs...
I'm stuck for the whole day on this.

If you supply the input as a StreamSource with no systemId property, then the system doesn't know where the input stream came from, which means it can't resolve any relative URIs contained in that input stream. You need to supply a base URI.

You haven't said which schema processor you are using and the details may vary. I think we had a case recently in Saxon where we found that the classpath: URI scheme was being correctly resolved to find other resources in the same JAR file, but this will not necessarily be the case for your situation; you may need to provide a URIResolver or SchemaResolver. But the first step is to make sure the base URI is known.

Based on Michael Kay observation, I implpemented a method to set the SystemId:

private static Source[] buildSources(String pattern) throws SAXException, IOException {
    List<Source> sources = new ArrayList<>();
    PathMatchingResourcePatternResolver patternResolver = new PathMatchingResourcePatternResolver();
    Resource[] resources = patternResolver.getResources(pattern);

    for (Resource resource : resources) {
        StreamSource dtd = new StreamSource(resource.getInputStream());
        dtd.setSystemId(resource.getURI().toString());
        sources.add(dtd);
    }
    return sources.toArray(new Source[sources.size()]);

}

Pattern looks like this:
"classpath:xsd/BASIC-WL_XSD/**/*.xsd"

xsd files are stored in resources folder ...