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。