不借助第三方类库，使用JDK自带API操作XML

先放2个主要方法：

import java.io.StringReader;import java.io.StringWriter;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.transform.Source;import javax.xml.transform.Transformer;import javax.xml.transform.TransformerFactory;import javax.xml.transform.dom.DOMSource;import javax.xml.transform.stream.StreamResult;import org.w3c.dom.Document;import org.xml.sax.InputSource;public class Test {public String domToString(Document doc) throws Exception {Transformer tf = TransformerFactory.newInstance().newTransformer();StringWriter sw = new StringWriter();Source source = new DOMSource(doc);tf.transform(source, new StreamResult(sw));return sw.toString();}public Document stringToDom(String xml) throws Exception {DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();InputSource is = new InputSource(new StringReader(xml));return db.parse(is);}}