运行出错,,

运行代码如下

package com.imooc.dmtest.test;

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.soap.Node;

import org.w3c.dom.Document;

import org.w3c.dom.NamedNodeMap;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

public class DOMTest {

public static void main(String[] args) {

// TODO Auto-generated method stub

DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();

try {

DocumentBuilder db=dbf.newDocumentBuilder();

try {

Document document=db.parse("books.xml");

NodeList bookList=document.getElementsByTagName("book");

 System.out.println(bookList.getLength()+"本书");

 for(int i=0;i<bookList.getLength();i++)

{

    Node book =  (Node) bookList.item(i);

NamedNodeMap attrs=book.getAttributes();

System.out.println("共有几个节点"+attrs.getLength());

}

} catch (SAXException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

} catch (ParserConfigurationException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

显示出错，不知道为什么？