java解析xml文件

JDK API中提供了3种方式解析XML，分别为DOM、SAX、XPath。

目录：

1. DOM
2. XPath：Mybaties中采用XPath方式解析XML文件的配置信息。
3. SAX

一.DOM

studentx.xml

<?xml version="1.0"?> 
<students> 
  <student> 
    <name>John</name> 
    <grade>B</grade> 
    <age>12</age> 
  </student> 
  <student> 
    <name>Mary</name> 
    <grade>A</grade> 
    <age>11</age> 
  </student> 
  <student> 
    <name>Simon</name> 
    <grade>A</grade> 
    <age>18</age> 
  </student> 
</students>

XMLParser.java

import java.io.File;  
import javax.xml.parsers.DocumentBuilder;  
import javax.xml.parsers.DocumentBuilderFactory;  
   
import org.w3c.dom.Document;  
import org.w3c.dom.Element;  
import org.w3c.dom.Node;  
import org.w3c.dom.NodeList;  
   
public class XMLParser {  
   
  public void getAllUserNames(String fileName) {  
    try {
      //1.获得一个文档解析器工厂：定义工厂API,使应用程序能够从XML文档获取生成DOM对象树的解析器
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
      //2.获得一个文档解析器：定义从XML文档获取DOM文档实例的API。 使用这个类，应用程序员可以从XML获得一个Document 。
      DocumentBuilder db = dbf.newDocumentBuilder();  

      File file = new File(fileName);  
      if (file.exists()) {  
    	//3.解析器解析xmL文件，获得一个DOM文档
        Document doc = db.parse(file);  
        
        //4.通过DOM文档获取根结点元素，并打印
        Element docEle = doc.getDocumentElement();  
        System.out.println("Root element of the document: "+ docEle.getNodeName());  
   
        //5.通过DOM文档根据标签名获取所有其对应的结点，并将其存储在NodeList抽象集合中
        NodeList studentList = docEle.getElementsByTagName("student");  
        System.out.println("Total students: " + studentList.getLength());  
 
        //6.打印"student"结点下所有的结点信息
        if (studentList != null && studentList.getLength() > 0) {  
          for (int i = 0; i < studentList.getLength(); i++) {  
        	  
        	//7.遍历一个"student"结点
            Node node = studentList.item(i);  
   
            //8.node.getNodeType() == Node.ELEMENT_NODE，表示node结点是一个Element(一组)
            if (node.getNodeType() == Node.ELEMENT_NODE) {  
              System.out.println("=====================");  
              
              Element e = (Element) node;  
              NodeList nodeList = e.getElementsByTagName("name");  
              System.out.println("Name: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());  
   
              nodeList = e.getElementsByTagName("grade");
              System.out.println("Grade: "+nodeList.item(0).getChildNodes().item(0)  .getNodeValue());  
              
              nodeList = e.getElementsByTagName("age");  
              System.out.println("Age: "+ nodeList.item(0).getChildNodes().item(0).getNodeValue());  
            }  
          }  
        } else {  
          ;  
        }  
      }  
    } catch (Exception e) {  
      System.out.println(e);  
    }  
  }  
  
  public static void main(String[] args) {  
    XMLParser parser = new XMLParser();  
    parser.getAllUserNames("./src/students.xml");  
  }  
}

三.XPath方式

users.xml

<?xml version="1.0"?> 
<users>
	<user id="1">
		<name>张三</name>
		<createTime>2018-10-15</createTime>
		<password>123</password>
		<phone>10086</phone>
		<nickName>阿毛</nickName>
	</user>
	<user id="2">
		<name>李四</name>
		<createTime>2018-10-15</createTime>
		<password>234</password>
		<phone>12306</phone>
		<nickName>二狗子</nickName>
	</user>
</users>

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class UserEntity {
	private Long id;
	private String name;
	private Date createTime;
	private String password;
	private String phone;
	private String nickName;

	static UserEntity buildUserEntity(String id, String name, String createTime, String password, String phone,
			String nickName) throws ParseException {
		UserEntity user=new UserEntity();
		user.id=Long.valueOf(id);
		user.name=name;
		user.createTime=new SimpleDateFormat("yyyy-MM-dd").parse(createTime);
		user.password=password;
		user.nickName=nickName;
		return user;
	}
	
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return id+"-"+name+"-"+createTime+"-"+password+"-"+nickName;
	}
}

import java.io.File;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;  
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;  
import org.w3c.dom.Element;  
import org.w3c.dom.Node;  
import org.w3c.dom.NodeList;  
   
public class XMLParser {  
   
  public void getAllUserNames(String fileName) {  
    try {
      //1.获得一个文档解析器工厂：定义工厂API,使应用程序能够从XML文档获取生成DOM对象树的解析器
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
      //2.获得一个文档解析器：定义从XML文档获取DOM文档实例的API。 使用这个类，应用程序员可以从XML获得一个Document 。
      DocumentBuilder builder = dbf.newDocumentBuilder();  
      File file=new File(fileName);
      //3.通过解析器解析xml文件，获得一个文档对象
      Document document=builder.parse(file);
      
      //4.获取新的XPathFactory实例
      XPathFactory xpathFactory=XPathFactory.newInstance();
      //5.一个XPathFactory实例可以用来创建XPath对象
      XPath xpath=xpathFactory.newXPath();
      //6.xpath根据根结点"users"标签解析document文档
      NodeList nodeList=(NodeList) xpath.evaluate("/users/*", document,XPathConstants.NODESET);
      
      //7.获取一个ArrayList实例用来存储UserEntity对象
      List<UserEntity> userList=new ArrayList<UserEntity>();
     
      //8.获取所有的user结点
      for(int i=1;i<nodeList.getLength()+1;i++) {
    	String path="/users/user["+i+"]";
    	String id=(String) xpath.evaluate(path+"/@id", document,XPathConstants.STRING);
    	String name=(String) xpath.evaluate(path+"/name", document,XPathConstants.STRING);
    	String createTime=(String) xpath.evaluate(path+"/createTime", document,XPathConstants.STRING);
    	String password=(String) xpath.evaluate(path+"/password", document,XPathConstants.STRING);
    	String phone=(String) xpath.evaluate(path+"/phone", document,XPathConstants.STRING);
    	String nickName=(String) xpath.evaluate(path+"/nickName", document,XPathConstants.STRING);
    	
    	//调用buildUserEntity()方法构建UserEntity对象
    	UserEntity userEntity=UserEntity.buildUserEntity(id,name,createTime,password,phone,nickName);
    	userList.add(userEntity);
    	
      }
      
      for(UserEntity user:userList) {
    	  System.out.println(user);
      }
      
    }catch(Exception e){
    	e.getMessage();
    }
      
  }  

	public static void main(String[] args) {  
	    XMLParser parser = new XMLParser();  
	    parser.getAllUserNames("./src/users.xml");  
	}  
}