XML解析问题

看如下代码
Java code:

package onlyfun.caterpillar;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class XMLServlet extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String xml = readXMLfromRequestBody(request);
Document xmlDoc = null;
try {
DocumentBuilder builder = DocumentBuilderFactory.newInstance()
.newDocumentBuilder();
xmlDoc = builder.parse(new ByteArrayInputStream(xml.getBytes()));
} catch (ParserConfigurationException e) {
System.out.println(e);
} catch (SAXException e) {
System.out.println(e);
}
String responseXML = prepareXMLResponse(xmlDoc);
responseXML = responseXML + "</responses>";
response.setContentType("text/xml");
response.getWriter().print(responseXML);
}

private String readXMLfromRequestBody(HttpServl