java如何解析/读取xml文件

<?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>

package net.viralpatel.java.xmlparser;  
  
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 {  
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
      DocumentBuilder db = dbf.newDocumentBuilder();  
      File file = new File(fileName);  
      if (file.exists()) {  
        Document doc = db.parse(file);  
        Element docEle = doc.getDocumentElement();  
  
        // Print root element of the document  
        System.out.println("Root element of the document: " 
            + docEle.getNodeName());  
  
        NodeList studentList = docEle.getElementsByTagName("student");  
  
        // Print total student elements in document  
        System.out  
            .println("Total students: " + studentList.getLength());  
  
        if (studentList != null && studentList.getLength() > 0) {  
          for (int i = 0; i < studentList.getLength(); i++) {  
  
            Node node = studentList.item(i);  
  
            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 {  
          System.exit(1);  
        }  
      }  
    } catch (Exception e) {  
      System.out.println(e);  
    }  
  }  
  public static void main(String[] args) {  
  
    XMLParser parser = new XMLParser();  
    parser.getAllUserNames("c:\\test.xml");  
  }  
}