DOM生成和解析xml

     本文主要代码示例DOM生成和解析xml，讨论下空值问题。

     Java资料里讲解DOM的东西很多，程序里也经常需要以xml形式保存和读取数据，但在解析类似这样的空值节点时，报出异常，会使得解析程序终止。有人的解决方案是，在保存时给每个值追加一个无意义字符串在后面，使得所有节点皆不空值，读取时，再减掉尾部的字符。保存累赘信息以回避技术问题，此码农之大忌，高手见笑。

一 生成xml   恐怕需要添加crimson.jar

   最后效果是 ：    
  
<?xml version="1.0" encoding="GBK"?><root> <student sex="男"> <name>张三</name> <phone>1234567</phone> </student> <student sex="男"> <name>李四</name> <phone></phone> </student></root>

    java代码

      package com.xml.write;import java.io.FileOutputStream;import java.io.OutputStreamWriter;import java.io.Serializable;import java.util.Vector;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.apache.crimson.tree.XmlDocument;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Text;public class XCreator {/** *创建xml的一个类 * @throws Exception  */public static void main(String[] args) throws Exception {drive() ;}private static void writeXML(String output,Vector vec)throws Exception{DocumentBuilder docBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();Document doc = docBuilder. newDocument();Element root = doc.createElement("root");doc.appendChild(root);for(int i = 0; i<vec.size() ;i++){StudentBean studentBean =(StudentBean)vec.get(i);Element student = doc.createElement("student");student.setAttribute("sex", studentBean.sex);root.appendChild(student);Element name = doc.createElement("name");student.appendChild(name);Text tName = doc.createTextNode(studentBean.name);name.appendChild(tName);Element phone =doc.createElement("phone");student.appendChild(phone);Text tPhone = doc.createTextNode(studentBean.phone);phone.appendChild(tPhone);}FileOutputStream outStream = new FileOutputStream(output);OutputStreamWriter outWriter = new OutputStreamWriter(outStream);((XmlDocument)doc).write(outWriter,"GBK");outWriter.close();outStream.close();}private static void drive()throws Exception{Vector vec = new Vector();StudentBean student = null;student = new StudentBean("张三","男","1234567");//student.phone =null;vec.addElement(student);vec.addElement(new StudentBean("李四","男",""));writeXML("config//stu.txt", vec);}}class StudentBean implements Serializable{public StudentBean(String _name,String _sex,String _phone){name = _name;sex =_sex ;phone = _phone ;}String name;String sex;String phone;} 

 

    

 

二  解析xml 

    

     代码如下：

     package com.read;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.parsers.ParserConfigurationException;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NodeList;import org.xml.sax.SAXException;public class ReadBooks {/** * @param args */public static void main(String[] args) {DomParse();}public static void DomParse() {DocumentBuilderFactory domfac = DocumentBuilderFactory.newInstance();try {DocumentBuilder dombuilder = domfac.newDocumentBuilder();InputStream is = new FileInputStream("config/stu.txt");Document doc = dombuilder.parse(is);Element root = doc.getDocumentElement();NodeList stus = root.getChildNodes();if (stus != null) {for (int i = 0; i < stus.getLength(); i++) {Node stu = stus.item(i);if (stu.getNodeType() == Node.ELEMENT_NODE) {String email = stu.getAttributes().getNamedItem("sex").getNodeValue();System.out.println(email);for (Node node = stu.getFirstChild(); node != null; node = node.getNextSibling()) {if (node.getNodeType() == Node.ELEMENT_NODE) {if (node.getNodeName().equals("name")) {String name1 = node.getFirstChild().getNodeValue();System.out.println(name1);}//if (node.getNodeName().equals("phone")) {//String price = node.getFirstChild()//.getNodeValue();//System.out.println(price);//}if(node.getNodeName().equals("phone")){Node n =node.getFirstChild();if(n!=null){String pub = node.getFirstChild().getNodeValue();System.out.println(pub);}}}}}}}} catch (ParserConfigurationException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} catch (SAXException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}} 
    注意在<student sex="男">
    <name>李四</name>
    <phone></phone>
    </student>节点中，有空值 ，读取里加个判断 Node n =node.getFirstChild();   if(n!=null)… 即可。