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");  
  }  
}