SAX方式解析XML

SAX方式解析XML原理

SAX的工作方式简单地说就是对文档进行顺序扫描，当扫描到文档（document）开始与结束,元素（Element）开始与结束、文档（document）结束等地方时通知事件处理函数，由事件处理函数做相应的动作，然后继续同样的扫描，直至文档结束。

优点：消耗资源比较少；适合大文件解析；

缺点：只能读取不能修改；开发复杂；

SAX方式解析XML示例

<?xml version="1.0" encoding="UTF-8"?>
<student id="001">
    <name>张三</name>
    <sex>男</sex>
    <age>20</age>
</student>

SAX01解析：

package com.java1234.xml;

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

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

public class SAX01 extends DefaultHandler{

    @Override
    public void startDocument() throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("<?xml version="1.0" encoding="UTF-8"?>");
    }

    @Override
    public void endDocument() throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("文档加载完毕！");
    }

    @Override
    public void startElement(String uri, String localName, String qName, 
            Attributes attributes) throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("元素节点开始加载"+qName);
    }

    @Override
    public void endElement(String uri, String localName,
            String qName) throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("元素节点结束加载"+qName);
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("扫描文本节点"+new String(ch,start,length));
    }
    
    public static void main(String[] args) throws Exception {
        SAXParserFactory factory=SAXParserFactory.newInstance();
        SAXParser parser=factory.newSAXParser();
        parser.parse("src/demo01.xml", new SAX01());
    }
}

解析更加复杂的信息；例如形成一个类重新输出类里面的数值啥的！

Student类

package com.java1234.model;

public class Student {
    private String name;
    private String sex;
    private String id;
    private int age;
    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 String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return this.id+","+this.name+","+this.age+","+this.sex;//重写toString 方法
    }
    
}

XML如下：

<?xml version="1.0" encoding="UTF-8"?>
<students>
    <student id="001">
        <name>张三</name>
        <sex>男</sex>
        <age>20</age>
    </student>
    <student id="002">
        <name>李四</name>
        <sex>女</sex>
        <age>18</age>
    </student>
</students>

package com.java1234.xml;

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

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

import com.java1234.model.Student;

public class SAX3 extends DefaultHandler{
    private List<Student>students=null;
    private Student student=null;
    private String tag=null;//标记上一个节点
    
    @Override
    public void startDocument() throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("开始读取学生信息");
        students=new ArrayList<Student>();
    }

    @Override
    public void endDocument() throws SAXException {
        // TODO Auto-generated method stub
        System.out.println("
 学生信息读取完毕");
    }

    @Override
    public void startElement(String uri, String localName, String qName, 
            Attributes attributes) throws SAXException {
        // TODO Auto-generated method stub
        //attributes 属性节点操作
        if("student".equals(qName)){
            student=new Student();
            student.setId(attributes.getValue(0));
        }
        tag=qName;
    }

    @Override
    public void endElement(String uri, String localName,
            String qName) throws SAXException {
        // TODO Auto-generated method stub
        if("student".equals(qName)){
            students.add(student);
            student=null;
        }
        tag=null;
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        // TODO Auto-generated method stub
        if(tag!=null){
            String content=new String(ch,start,length);
            if("name".equals(tag)){
                student.setName(content);
            }else if("age".equals(tag)){
                student.setAge(Integer.parseInt(content));
            }else if("sex".equals(tag)){
                student.setSex(content);
            }
        }
    }
    
    public static void main(String[] args) throws Exception {
        SAXParserFactory factory=SAXParserFactory.newInstance();
        SAXParser parser=factory.newSAXParser();
        SAX3 sax3=new SAX3();
        parser.parse("src/students.xml", sax3);
        for(Student s:sax3.students){
            System.out.println(s);
        }
    }
    
    
    
}

结果如下所示：