W3CDomHandler.java 文件源码

public Element getElement(DOMResult r) {
    // JAXP spec is ambiguous about what really happens in this case,
    // so work defensively
    Node n = r.getNode();
    if( n instanceof Document ) {
        return ((Document)n).getDocumentElement();
    }
    if( n instanceof Element )
        return (Element)n;
    if( n instanceof DocumentFragment )
        return (Element)n.getChildNodes().item(0);

    // if the result object contains something strange,
    // it is not a user problem, but it is a JAXB provider's problem.
    // That's why we throw a runtime exception.
    throw new IllegalStateException(n.toString());
}