Code using net.sf.saxon.functions.DeepEqual.deepEquals to compare the equality of two XdmNodes. Very saxon specific. Is this the deepEquals method theadsafe?

DeepEqualsWrapper.java

import net.sf.saxon.Configuration;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.expr.sort.CodepointCollator;
import net.sf.saxon.expr.sort.GenericAtomicComparer;
import net.sf.saxon.functions.DeepEqual;
import net.sf.saxon.lib.UnfailingErrorListener;
import net.sf.saxon.s9api.Processor;
import net.sf.saxon.s9api.XdmNode;
import net.sf.saxon.trans.XPathException;
import javax.xml.transform.TransformerException;

public class DeepEqualsWrapper {
    private final Processor proc;

    // Singleton processor created within a spring context.
    public DeepEqualsWrapper(Processor proc) {
        proc = this.proc;
    }

    private class LocalErrorListener implements UnfailingErrorListener {
        private final StringBuilder errors;

        LocalErrorListener() {
            errors = new StringBuilder();
        }


        @Override
        public void warning(TransformerException e) {
            errors.append(e.getMessage());
        }

        @Override
        public void error(TransformerException e) {
            errors.append(e.getMessage());
        }

        @Override
        public void fatalError(TransformerException e) {
            errors.append(e.getMessage());
        }

        public String getErrors() {
            return errors.toString();
        }
    }

    // XdmNodes are created by the same Processor that has been passed into this class.
    public String getNodeDifferences(XdmNode node1, XdmNode node2) throws XPathException {
        Configuration config = new Configuration();
        LocalErrorListener errorListener = new LocalErrorListener();
        config.setErrorListener(errorListener);
        XPathContext context = config.getConversionContext().newContext();
        GenericAtomicComparer comparer = new GenericAtomicComparer(CodepointCollator.getInstance(), context);
        boolean isEqual = DeepEqual.deepEquals(
                node1.getUnderlyingNode(),
                node2.getUnderlyingNode(),
                comparer,
                config,
                DeepEqual.INCLUDE_PREFIXES | DeepEqual.EXCLUDE_WHITESPACE_TEXT_NODES | DeepEqual.INCLUDE_PROCESSING_INSTRUCTIONS);

        String differences;
        if (isEqual) {
            differences = "";
        } else {
            differences = errorListener.getErrors();
        }

        return differences;

    }
}