e538. determining if an attribute was supplied in a dom element.txt

这里面包含了一百多个JAVA源文件

In the case of an attribute with a default value, it is possible to determine if the attribute was explicitly supplied in the original XML document or automatically created when it was parsed. 
Note: If the attribute value is changed in the DOM document, the attributed is considered to have been supplied, even if the new value is the same as the default value. 

    // Get Attr node
    Attr attr = (Attr)element.getAttributeNode("attrName");
    boolean wasSpecified = attr != null && attr.getSpecified();