sax解析xml文件实例一(注意endElement 内部最后 currentTag=null)

本文重点两点：1.再一次解析一个xml,验证之前的理解。 2. 发现endElement内最后一定要 currentTag = null

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注意：一定要在endElement内最后currentTag = null .

原因：如前一篇所讲，对于非根节点(eg :<name>)，在经历 startElement(currentTag = name),characters (currentTag = name,currentValue = "刘德华"),endElement()后，还会触发一次 characters 。

所以，1. 若endElement内不currentTag = null 的话，那endElement后的currentTag 还是 “name”,然后再触发一次 characters,但此时 characters 内的 new String (ch,start,length) 是空值，不是之前第二步的"刘德华"，这样的话本来在第二步中已经赋值的 name = 刘德华，会在第四步中 name = 空。

2. 若endElement内最后设置currentTag = null,则触发第四步 characters时，原来在第二步已经被保存的name = "刘德华" 就不会被更新为空值。因为根据characters内的判断条件可知，currentTag = 空时不进行操作。

总结一句话：在解析一个node节点结束标签(例如</name>)时，会触发endElement和characters方法，要在endElement方法内，将currentTag = null .

(本例中可以把 endElement内最后的 currentTag = null 删除作为测试)

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student.xml

<?xml version="1.0" encoding="UTF-8"?>
<StudentInfo>  
    <student>  
        <name>刘德华</name>  
        <sex>男</sex>  
        <lesson>  
            <lessonName>Spring整合开发</lessonName>  
            <lessonscore>85</lessonscore>  
        </lesson>  
        <lesson>  
            <lessonName>轻量级J2EE应用开发</lessonName>  
            <lessonscore>95</lessonscore>  
        </lesson>  
        <lesson>  
            <lessonName>Ajax应用开发</lessonName>  
            <lessonscore>80</lessonscore>  
        </lesson>  
    </student> 	 
    <student>  
        <name>宋慧乔</name>  
        <sex>女</sex>  
        <lesson>  
            <lessonName>Spring整合开发</lessonName>  
            <lessonscore>80</lessonscore>  
        </lesson>  
        <lesson>  
            <lessonName>轻量级J2EE应用开发</lessonName>  
            <lessonscore>85</lessonscore>  
        </lesson>  
        <lesson>  
            <lessonName>Ajax应用开发</lessonName>  
            <lessonscore>90</lessonscore>  
        </lesson>  
    </student>  
</StudentInfo>

程序运行结果：

name :宋慧乔
sex :女
Ajax应用开发=90
Spring整合开发=80
轻量级J2EE应用开发=85
-----------------------------------
name :刘德华
sex :男
Spring整合开发=85
轻量级J2EE应用开发=95
Ajax应用开发=80
-----------------------------------

客户端eclipse java工程android_sax_xml2目录（左边）和服务器端 myeclipse web工程myhttp目录

客户端 Lesson.java

package com.sax.data;

import java.util.HashSet;

public class Lesson {

	private String lessonName ; //课程名称
	private String lessonscore ; //课程分数
	
	public Lesson() {
		// TODO Auto-generated constructor stub
	}

	public String getLessonName() {
		return lessonName;
	}

	public void setLessonName(String lessonName) {
		this.lessonName = lessonName;
	}

	public String getLessonscore() {
		return lessonscore;
	}

	public void setLessonscore(String lessonscore) {
		this.lessonscore = lessonscore;
	}
	
	
}

客户端 Student.java

package com.sax.data;


import java.util.Set;

public class Student {

	private String name ;
	private String sex;
	private Set<Lesson> lessons;
	
	public Student() {
		// TODO Auto-generated constructor stub
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public Set<Lesson> getLessons() {
		return lessons;
	}

	public void setLessons(Set<Lesson> lessons) {
		this.lessons = lessons;
	}
	
	

}

客户端 MyHandler.java

package com.sax.handler;

import java.util.HashSet;
import java.util.Set;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

import com.sax.data.Lesson;
import com.sax.data.Student;

public class MyHandler extends DefaultHandler {

	private Lesson lesson;
	private Set<Lesson> lessons;//每个学生对应的所有的lesson对象
	private Student student;
	private Set<Student> students;  //所有的student对象
	
	private String currentTag;          //当前访问到的节点名称
	
	/*nodeName 为一查询标签，让用户自己设定。从构造函数传入。本文nodeName = student .
	 * 为了直观理解解析过程，就直接用"student"字符串，而不是用nodeName.
	 * 实际上应该用nodeName 代替 "student"字符串
	 * */
	private String nodeName;           
	
	public MyHandler(String nodeName) {
		 //这里nodeName由用户输入 本程序 为"student",下文里的 "student"字符串 其实应该用nodeName来代替
		this.nodeName = nodeName;  
	}
	
	
	
	public Set<Student> getStudents() {
		return students;
	}



	@Override
	public void startDocument() throws SAXException {
		// TODO Auto-generated method stub
		
		students = new HashSet<Student>();
		System.out.println("--startDocument--");
		super.startDocument();
	}
	
	@Override
	public void startElement(String url,String localName,String qName,Attributes attributes) throws SAXException {
		// TODO Auto-generated method stub
		
		currentTag = qName;	
		System.out.println("startElement currentTag :"+currentTag);
	
		if ("student".equals(currentTag)) {
			student = new Student();
			lessons = new HashSet<Lesson>();
			
		}
		if ("lesson".equals(currentTag)) {
			lesson = new Lesson() ;
		}		
		
	}
	@Override
	public void characters(char[] ch,int start,int length) throws SAXException {
		
		String currentValue = new String(ch,length); 
		
		System.out.println("characters currentTag :"+currentTag+",currentValue :"+currentValue);
	
		if (currentTag=="name") {
			student.setName(currentValue);
		}
		if (currentTag == "sex") {
			student.setSex(currentValue);
		}
		if (currentTag == "lessonName") {
			lesson.setLessonName(currentValue);
		}
		if (currentTag == "lessonscore") {
			lesson.setLessonscore(currentValue);
			
		}
	}
	@Override
	public void endElement(String url,String qName)
			throws SAXException {
		currentTag = qName;
		System.out.println("endElement currentTag :"+currentTag);
		/*
		 * if (currentTag == "lesson" && lesson != null) {
			lessons.add(lesson);
			lesson = null;
		}
		if(currentTag == "student" && lessons != null){
			student.setLessons(lessons);
			lessons = null;			
			
		}
		if (currentTag == "student" && student != null) {
			students.add(student);
			student = null;
		}
		 * */
	
		 if (currentTag == "lesson") {
				lessons.add(lesson);
			
			}
			if(currentTag == "student"){
				student.setLessons(lessons);				
			}
			if (currentTag == "student") {
				students.add(student);
				
			}
		/*
		 * 为了 characters方法中用作标记，因为endElement后还会触发characters方法，
		 * 所以，在endElement中最后要currentTag = null;
		 * */
		currentTag = null;    
	}
	@Override
	public void endDocument() throws SAXException {
		// TODO Auto-generated method stub
		System.out.println("--endDocument--");
		super.endDocument();
	}
}

客户端：SaxService.java

package com.sax.service;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.SAXException;

import com.sax.data.Student;
import com.sax.handler.MyHandler;

public class SaxService {

	public SaxService() {
		// TODO Auto-generated constructor stub
	}

	public static Set<Student> readXML(
			InputStream inputStream,String nodeName) {

		Set<Student> students = new HashSet<Student>();
		
		try {
			SAXParserFactory spf = SAXParserFactory.newInstance();
			SAXParser parser = spf.newSAXParser();			
			MyHandler handler = new MyHandler(nodeName);
			parser.parse(inputStream,handler);
			students = handler.getStudents();
			inputStream.close();			
		} 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();
		}
		
		return students;
		

	}
}

客户端： HttpUtils.java

package com.sax.http;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class HttpUtils {

	public HttpUtils() {
		// TODO Auto-generated constructor stub
	}

	public static InputStream getXML(String path) {

		InputStream inputStream = null;

		try {
			URL url = new URL(path);

			if (url != null) {
				HttpURLConnection httpURLConnection = (HttpURLConnection) url
						.openConnection();
				httpURLConnection.setConnectTimeout(3000);
				httpURLConnection.setDoInput(true); // 从服务器获取数据
				httpURLConnection.setRequestMethod("GET");

				int responseCode = httpURLConnection.getResponseCode();

				if (responseCode == 200) {
					inputStream = httpURLConnection.getInputStream();
				}
			}

		} catch (MalformedURLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		return inputStream;

	}

}

客户端 Test.java

package com.sax.test;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import com.sax.data.Lesson;
import com.sax.data.Student;
import com.sax.http.HttpUtils;
import com.sax.service.SaxService;

public class Test {

	public Test() {
		// TODO Auto-generated constructor stub
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub		
		
		Set<Student> students = new HashSet<Student>();
		InputStream inputStream = HttpUtils.getXML("http://192.168.0.102:8080/myhttp/student.xml");	
	
		students = SaxService.readXML(inputStream,"student");
		
		for (Student stu : students) {
			System.out.println("name :"+stu.getName());
			System.out.println("sex :"+stu.getSex());
			Set<Lesson> lessons = stu.getLessons();
			for(Lesson lesson:lessons){
				System.out.println(lesson.getLessonName()+"="+lesson.getLessonscore());				
			}
			System.out.println("-----------------------------------");
		}

	}

}

服务器端 LoginAction.java

package com.login.manager;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginAction extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public LoginAction() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	public void doGet(HttpServletRequest request,HttpServletResponse response)
			throws ServletException,IOException {

		this.doPost(request,response);
	}

	/**
	 * The doPost method of the servlet. <br>
	 * 
	 * This method is called when a form has its tag value method equals to
	 * post.
	 * 
	 * @param request
	 *            the request send by the client to the server
	 * @param response
	 *            the response send by the server to the client
	 * @throws ServletException
	 *             if an error occurred
	 * @throws IOException
	 *             if an error occurred
	 */
	public void doPost(HttpServletRequest request,IOException {

		response.setContentType("text/html;charset=utf-8");
		request.setCharacterEncoding("utf-8");
		response.setCharacterEncoding("utf-8");
		//客户端 HttpUtils并没有写request方法是post,但服务器端可自动识别
		String method = request.getMethod();
		System.out.println("request method :"+method);
		
		
		PrintWriter out = response.getWriter();
		String username = request.getParameter("username");
		System.out.println("-username->>"+username);
		
		String password = request.getParameter("password");
		System.out.println("-password->>"+password);

		if (username.equals("admin") && password.equals("123")) {
			// 表示服务器段返回的结果
			out.print("login is success !");

		} else {
			out.print("login is fail !");
		}

		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 * 
	 * @throws ServletException
	 *             if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

}

sax解析xml文件实例一(注意endElement 内部最后 currentTag=null)

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