java的xml解析,遇到以下问题,不知道如何解决

package xml;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.InputStream;
import java.util.Iterator;
import java.util.List;
public class XmlParser {
public static void main(String[] args) throws DocumentException {
SAXReader reader = new SAXReader();
//通过类的字节码对象获取一个给定资源并将该资源读取到流的通道
InputStream is = XmlParser.class.getResourceAsStream("f.xml");
//SAX 读取器从通道中读取一个文档对象
Document document = reader.read(is);
//获取文档的根元素,因为XML文档只会有一个根元素
Element root = document.getRootElement();
//获取根元素标签名
String tagname = root.getQualifiedName();
System.out.println("xml根标签名:" + tagname);
// //获取根元素的子元素
// List<Element> elements = root.elements();
// for(Element element:elements){
// //获取元素标签名
// String tagname = element.getQualifiedName();
// System.out.println(tagname);
// //获取属性
// List<Attribute> attributes = element.attributes();
// for(Attribute attribute:attributes){
// //获取属性名
// String attrname = attribute.getName();
// //获取属性值
// String value = attribute.getValue();
// System.out.println("属性:"+attrname+"-->"+value+"\t");
// }
// System.out.println();
// }
Iterator<Element> iterator = root.attributeIterator();
while(iterator.hasNext()){
//获取元素标签名
Element element = iterator.next();
String name = element.getQualifiedName();
System.out.println(name);
//获取属性
List<Attribute> attributes = element.attributes();
for(Attribute attribute:attributes){
//获取属性名
String attrname = attribute.getName();
//获取属性值
String value = attribute.getValue();
System.out.println("属性:"+attrname+"-->"+value+"\t");
}
System.out.println();
}
}
}
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE students SYSTEM "student.dtd">
<students>
<!-- <student>-->
<!-- <name>张三</name>-->
<!-- <age>20</age>-->
<!-- <sex>男</sex>-->
<!-- </student>-->
<student id="1" name="张三" age="20" sex="男" country="中国" />
<student id="2" name="张三" age="20" sex="男" />
<student id="3" name="张三" age="20" sex="男" />
</students>
<!ELEMENT students (student*) >
<!--<!ELEMENT student (name,age,sex) ANY>-->
<!--<!ELEMENT name (#PCDATA)>-->
<!--<!ELEMENT age (#PCDATA)>-->
<!--<!ELEMENT sex (#PCDATA)>-->
<!ELEMENT student EMPTY>
<!ATTLIST student id ID #REQUIRED>
<!ATTLIST student name CDATA>
<!ATTLIST student age CDATA>
<!ATTLIST student sex(男|女|其他) #IMPLIED>
<!ATTLIST student country(中国) CDATA #FIXED>