Unmarshaller with custom unescaping some symbols utf-8 and utf-16

Question

I have XML file where some symbols were incorrectly encoded because of mixing UTF-16 and UTF-8.

For example, symbol is encoded as �� (��) instead of (📞).

I want to unmarshal this XML file but it fails when Unmarshaller meet these incorrect symbols. If I decode only them with StringEscapeUtils#unescapeHtml4 (or StringEscapeUtils#unescapeXml) everything works correctly.

But I don't want to read XML to string then decode it and then unmarshal.

How I could do the same inside the unmarshalling process (not to read XML file to string before)?

I created a simple test to reproduce this:

public class XmlReaderTest {

    private static final Pattern HTML_UNICODE_REGEX = Pattern.compile("&#[a-zA-Z0-9]+;&#[a-zA-Z0-9]+;");

    @Test
    public void test() throws Exception {
        final Unmarshaller unmarshaller = JAXBContext.newInstance(Value.class).createUnmarshaller();
        final XMLInputFactory factory = createXmlInputFactory();

        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><value><name>&#55357;&#56542; &amp; &#128222; O&#771;</name></value>";

        XMLEventReader xmlReader = factory.createXMLEventReader(new StringReader(decodeHtmlEntities(xml)));
        Value result = (Value)unmarshaller.unmarshal(xmlReader);
        assert result.name.equals("\uD83D\uDCDE & \uD83D\uDCDE Õ");

        XMLEventReader xmlReader2 = factory.createXMLEventReader(new StringReader(xml));
        Value result2 = (Value)unmarshaller.unmarshal(xmlReader2); // ! exception
        assert result2.name.equals("\uD83D\uDCDE & \uD83D\uDCDE Õ");
    }

    @XmlRootElement(name = "value")
    private static class Value {
        @XmlElement
        public String name;
    }

    private String decodeHtmlEntities(String readerString) {
        StringBuffer unescapedString = new StringBuffer();

        Matcher regexMatcher = HTML_UNICODE_REGEX.matcher(readerString);
        while (regexMatcher.find()) {
            regexMatcher.appendReplacement(unescapedString, StringEscapeUtils.unescapeHtml4(regexMatcher.group()));
        }
        regexMatcher.appendTail(unescapedString);

        return unescapedString.toString();
    }

    private XMLInputFactory createXmlInputFactory() {
        XMLInputFactory factory = XMLInputFactory.newFactory();
        factory.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES, false);
        factory.setProperty(XMLInputFactory.SUPPORT_DTD, false);
        return factory;
    }
}