Import the right classes:

import org.apache.xerces.util.*;
import org.apache.xerces.xs.*;
import org.apache.xerces.xni.*;
import org.apache.xerces.xni.parser.*;
import org.apache.xerces.parsers.*;

Create the parser and set the right features (much like JAXP):

XMLParserConfiguration parser = new StandardParserConfiguration();
parser.setFeature("http://xml.org/sax/features/validation",true);
parser.setFeature("http://apache.org/xml/features/validation/schema",true);
parser.setFeature("http://apache.org/xml/features/validation/schema-full-checking",true);

Setup the catalog:

String [] catalogs = { "catalog.xml" };
XMLCatalogResolver resolver = new XMLCatalogResolver(catalogs);
parser.setEntityResolver(resolver);

Set your document and error handlers

parser.setDocumentHandler(new MyDocumentHandler());
// DefaultErrorHandler is a utility class from Xerces that sends
// errors to stderr.
parser.setErrorHandler(new DefaultErrorHandler());

Parse your document:

String uri = new File("doc.xml").toURI().toString();
XMLInputSource source = new XMLInputSource(null,uri,uri);
parser.parse(source);