sax中DefaultHander解析xml过程和先后顺序

发布时间：2020-12-16 05:02:31 所属栏目：百科来源：网络整理

导读：本文讲解三点：1. sax中DefaultHandler解析XML总体过程 2. sax中DefaultHandler解析XML非根node的先后顺序 3.sax中DefaultHandler解析XML根node先后顺序 (三点均通过实际程序测试出来，程序见下文) 一：sax中DefaultHandler解析XML总体过程 startDocument--

本文讲解三点：1. sax中DefaultHandler解析XML总体过程 2. sax中DefaultHandler解析XML非根node的先后顺序 3.sax中DefaultHandler解析XML根node先后顺序 (三点均通过实际程序测试出来，程序见下文)

一：sax中DefaultHandler解析XML总体过程

startDocument--->具体读到某个node（非根node和根node）的解析过程 --->endDocument 。

二：DefaultHandler 解析XML 的非根node是按顺序的四步（不管当前node是ElementNode[可有属性]还是TextNode）(非根node本测试程序如 person,name,age)：

第一步：startElement. (eg:startElement localName : qName : age)

第二步 : characters (eg:characters in age = 25)

第三步 : endElement (eg: endElement in )

第四步 : characters(eg: characters in null =!)

三：DefaultHandler 解析XML 的根node是按顺序的三步（本测试程序中根node为 persons)：

第一步：startElement. (eg:startElement localName : qName : persons)

第二步 : characters (eg:characters inpersons = !)

第三步 : endElement (eg:endElement in )

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使用org.sax.helper.DefaultHandler 解析XML,一般会调用以下六个方法，需要你重写。

1. 开始解析xml文档 startDocument

2.读到某个节点 startElement-->characters-->endElement-->characters (endElement后会再调用一次characters方法)

3.解析xml文档结束 endDocument

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org.sax.helper.DefaultHandler 解析XML 的算法思路(自己理解的)

对每一个非根节点node都要进行两项检查:1.检查是不是ElementNode(用startElement方法) ; 2.是不是TextNode(用characters方法)，遇到当前节点结尾时，调用endElement和characters方法。最关键的一句话：DefaultHandler会自动解析到下个节点，通过调用startElement方法。并把最新解析到的节点名称放在startElement(Strng url,Sting localName,String qName,Attributes attributes) 的qName中。

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测试程序：

客户端eclipse读取服务器端myeclpse的myhttp工程根目录下的persons.xml文件

persons.xml

<?xml version = "1.0" encoding = "UTF-8">
<persons>
	<person id="23">
		<name>黄老师</name>
		<age>26</age>
	</person>
	<person id="25">
		<name>杨老师</name>
		<age>28</age>
	</person>
</persons>

客户端程序运行结果：

--startDocument--
startElement localName: qName:persons
characters in persons=
	!
startElement localName: qName:person
characters in person=
		!
startElement localName: qName:name
characters in name=黄老师!
endElement in 
characters in null=
		!
startElement localName: qName:age
characters in age=26!
endElement in 
characters in null=
	!
endElement in 
characters in null=
	!
startElement localName: qName:person
characters in person=
		!
startElement localName: qName:name
characters in name=杨老师!
endElement in 
characters in null=
		!
startElement localName: qName:age
characters in age=28!
endElement in 
characters in null=
	!
endElement in 
characters in null=
!
endElement in 
--endDocument--
{name=黄老师,id=23,age=26}
{name=杨老师,id=25,age=28}

1.分析对每一个非根节点都会按顺序触发4个方法，如<age>和<person>;

对于<age>这个节点很直观可以看到，对于<person>其实也是如此，以person为黄老师为例: 刚开始解析到person节点(即解析到<person>时)，触发startElement和characters；当遍历完 name 和 age节点到达</person> 时，触发了 endElement 和 characters方法

2.而对于根节点<persons>只触发前三个方法，而不触发最后一个characters方法。

因为xml文档必须包含一个根节点，且只能包含一个根节点，即本xml的根节点为<persons>具有唯一性，所以当解析遇到</persons>时会知道整个xml文档已经解析完毕,所以不会触发characters方法。而是在endElement后直接触发endDocument方法。

客户端eclipse程序目录（左边），服务器端myeclipse程序目录（右边）

MyHandler2.java

package com.sax.handler;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

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

public class MyHandler2 extends DefaultHandler {

	private List<HashMap<String,String>> list = null;
	private HashMap<String,String> map = null;

	private String currentTag = null;
	private String nodeName = null;

	public MyHandler2(String nodeName) {
		// TODO Auto-generated constructor stub
		this.nodeName = nodeName;
	}

	public List<HashMap<String,String>> getList() {
		return list;
	}

	@Override
	public void startDocument() throws SAXException {
		System.out.println("--startDocument--");
		list = new ArrayList<HashMap<String,String>>();
	}

	@Override
	public void startElement(String url,String localName,Attributes attributes) throws SAXException {

		System.out.println("startElement localName: " + localName + "qName:"
				+ qName);
		currentTag = qName;
		if (nodeName.equals(qName)) { // nodeName 是 person,由构造函数传入。
			map = new HashMap<String,String>();
			map.put("id",attributes.getValue("id"));
		}
	}

	@Override
	public void characters(char[] arg0,int arg1,int arg2) throws SAXException {

		System.out.println("characters in " + currentTag + "="
				+ new String(arg0,arg1,arg2) + "!");

		if ("name".equals(currentTag)) {
			map.put("name",new String(arg0,arg2));
		}
		if ("age".equals(currentTag)) {
			map.put("age",arg2));
		}
	}

	@Override
	public void endElement(String url,String qName)
			throws SAXException {
		System.out.println("endElement in " + localName);
		if ("person".equals(qName)) {

			list.add(map);
		}
		currentTag = null;
	}

	@Override
	public void endDocument() throws SAXException {
		System.out.println("--endDocument--");
	}

}

SaxService.java

package com.sax.service;

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

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

import org.xml.sax.SAXException;

import com.sax.handler.MyHandler;
import com.sax.handler.MyHandler2;

public class SaxService {

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

	public static List<HashMap<String,String>> readXML(
			InputStream inputStream,String nodeName) {

		try {
			// 创建一个解析XML的工厂对象
			SAXParserFactory spf = SAXParserFactory.newInstance();
			SAXParser parser = spf.newSAXParser();
			// MyHandler handler = new MyHandler(nodeName);
			MyHandler2 handler = new MyHandler2(nodeName);

			parser.parse(inputStream,handler);
			inputStream.close();
			// return handler.getList();
			return handler.getList();

		} 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 null;

	}
}

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;

	}

}

Test.java

package com.sax.test;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import com.sax.handler.MyHandler;
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
		List<HashMap<String,String>> list = new ArrayList<HashMap<String,String>>();		
		
		InputStream inputStream = HttpUtils.getXML("http://192.168.0.102:8080/myhttp/persons.xml");	
	
		list = SaxService.readXML(inputStream,"person");
		
		for (HashMap<String,String> hashMap : list) {
			System.out.println(hashMap.toString());
		}
		
		
		

	}

}

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
	}

}

（编辑：李大同）

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