xml解析节点时，值全为null，谁帮下忙

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE pets[<!ELEMENT pets (dog,penguin)><!ELEMENT dog (love,health,rehealth,addlove)><!ELEMENT penguin (love,health,rehealth,addlove)>]><pets>    <dog>        <love>0</love>        <health>100</health>        <rehealth>5</rehealth>        <addlove>10</addlove>    </dog>    <penguin>        <love>0</love>        <health>100</health>        <rehealth>10</rehealth>        <addlove>15</addlove>    </penguin></pets>

package cn.jbit.Test;import java.io.IOException;import javax.xml.parsers.*;import org.w3c.dom.*;import org.xml.sax.SAXException;public class Test {    /**     * @param args     */    public static void main(String[] args) {                DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();                try {            DocumentBuilder db=dbf.newDocumentBuilder();            Document doc=db.parse("PetInfo.xml");            //获取根节点            Node pets=doc.getDocumentElement();            //获取根节点下的所有子节点            NodeList dogAndpenguin=pets.getChildNodes();            //开始遍历            for(int i=0;i<dogAndpenguin.getLength();i++){                                if(dogAndpenguin.item(i).getNodeType()==Node.ELEMENT_NODE){                    System.out.println(dogAndpenguin.item(i).getNodeName());                                        NodeList infos=dogAndpenguin.item(i).getChildNodes();                                        for(int j=0;j<infos.getLength();j++){                        if(infos.item(j).getNodeType()==Node.ELEMENT_NODE)                            System.out.println(infos.item(j).getNodeName());                            System.out.println(infos.item(j).getNodeValue());                    }                                    }                            }                                } catch (ParserConfigurationException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SAXException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }            }}