什么可能在我的xml中导致此stackoverflow？

Question

我正在针对已知架构验证xml并获得stackoverflow错误。我的xml出了什么问题？我应该寻找什么？从1.6 Java中找到的代码抛出了这个错误。

JAXBContext context = JAXBContext.newInstance(Root.class);
        Unmarshaller un = context.createUnmarshaller();
        SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
        URL resource = ClassLoader.getSystemResource("schema.xsd");
        if (resource == null) {
            throw new IllegalStateException("Could not find schema!");
        }
        Schema schema = schemaFactory.newSchema(resource);
        un.setSchema(schema);
        Root root = un.unmarshal(xml) // Error thrown here

错误：

    java.lang.StackOverflowError
        at com.sun.org.apache.xerces.internal.impl.xpath.regex.RegularExpression.matchString(RegularExpression.java:1878)
        at com.sun.org.apache.xerces.internal.impl.xpath.regex.RegularExpression.matchString(RegularExpression.java:1878)