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

------------------------------------------------------------------------------------------------------------------

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)

-----------------------------------------------------------------------------------------------------------------

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=90Spring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=95Ajax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;}@Overridepublic void startDocument() throws SAXException {// TODO Auto-generated method stubstudents = new HashSet<Student>();System.out.println("--startDocument--");super.startDocument();}@Overridepublic void startElement(String url, String localName, String qName,Attributes attributes) throws SAXException {// TODO Auto-generated method stubcurrentTag = 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() ;}}@Overridepublic void characters(char[] ch, int start, int length) throws SAXException {String currentValue = new String(ch, start, 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);}}@Overridepublic void endElement(String url, String localName, 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;    }@Overridepublic void endDocument() throws SAXException {// TODO Auto-generated method stubSystem.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 blocke.printStackTrace();} catch (SAXException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.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 blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.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 stubSet<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, HttpServletResponse response)throws ServletException, 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}}