关于xml中集合在遍历时一边查找一边删除出现的问题的解决思路的例子

package com.lee.dao;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import com.lee.domain.Student;
import com.lee.exception.StudentNotExistException;
import com.lee.xmlutils.XmlUtils;

public class StudentDao {
	//	按姓名添加学生
	public void add(Student s){
		Document document ;
		try {
			document = XmlUtils.getDocument();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException(e);
		}
		//	创建自定义的封装的标签
		Element student_tag = document.createElement("student");
		student_tag.setAttribute("examid", s.getExamid());
		student_tag.setAttribute("idcard", s.getIdcard());
		
		Element name = document.createElement("name");
//		name.setNodeValue(s.getName());
		name.setTextContent(s.getName());
		
		Element location = document.createElement("location");
//		location.setNodeValue(s.getLocation());
		location.setTextContent(s.getLocation());
		
		Element grade = document.createElement("grade");
//		grade.setNodeValue(Double.parseDouble(s.getGrade()));
		grade.setTextContent(String.valueOf(s.getGrade()));
		
		student_tag.appendChild(name);
		student_tag.appendChild(location);
		student_tag.appendChild(grade);
		
		document.getElementsByTagName("exam").item(0).appendChild(student_tag);
		
		try {
			XmlUtils.write2Xml(document);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException(e);
		}
	}
	
	//	按身份证号删除学生
	//	从name标签中查找遍历，是否存在于与传过来的参数一致的值
	//	找到后，因为idcard是student的子节点，student是exam的子节点，需要删除的是student
	//	因此，拿到idcard的父节点的父节点exam，删除子节点student
	public void delete(String idcard) throws StudentNotExistException{
		Document document ;
		boolean isDelete = false;
		try {
			document = XmlUtils.getDocument();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException();
		}
		//	nodeList是得到所有的name标签的集合
		//	nodeList.item是从name标签的集合中取出第几个
		//	nodeList.item.getTextContent拿到此节点的文本内容<name>文本内容</name>
		//	如何同时删除多个数据？？？？？如果删除后，找不到idcard了呢，此时出错？？？？？？
		//	删除的方法出错了
		
		//	找到错误的原因：
		//	nodeList原集合中有5个元素，a,b,c,d,e
		//	遍历nodeList.item(i)得到student_tag
		//	1.1	当nodeList.item(0)时，删除5个元素中的第1个元素a,剩余b,c,d,e
		//	1.2	当nodeList.item(1)时，删除4个元素中的第2个元素c,剩余b,d,e
		//	由上可以发现，遍历的时候，应该需要减去被删除的个数
		//	即修改的正确方式为：
		//	nodeList.item(i - j)得到student_tag
		//	1.1	当nodeList.item(0 - 0)时，删除5个元素中的第1个元素a,剩余b,c,d,e
		//	因为删除掉一个元素,所以j++
		//	1.2	当nodeList.item(1 - 1)时，删除4个元素中的第1个元素b,剩余c,d,e
		//	于是不会出现空指针，修正了上述的错误
		NodeList nodeList = document.getElementsByTagName("student");
		for(int i = 0, len = nodeList.getLength(), j = 0; i < len; i++){
			System.out.println("Length(): " + nodeList.getLength());
			System.out.println("i: " + i);
			System.out.println("i - j: " + (i - j));
			Element student_tag = (Element) nodeList.item(i - j);	
			System.out.println(student_tag.getAttribute("idcard"));
			if(student_tag.getAttribute("idcard").equals(idcard)){
				student_tag.getParentNode().removeChild(nodeList.item(i - j));
				isDelete = true;
				j++;
			}
		}
		if(isDelete){
			try {
				XmlUtils.write2Xml(document);
				return;
			}catch (StudentNotExistException e) {
				// TODO Auto-generated catch block
				throw e;
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
				
			}
		}

//		
//		if(isDelete){
//			try {
//				XmlUtils.write2Xml(document);
//			} catch (Exception e) {
//				// TODO Auto-generated catch block
//				e.printStackTrace();
//				throw new RuntimeException(e);
//			}
//		}else{
//			try {
//				throw new StudentNotExistException(idcard + "不存在");
//			} catch (StudentNotExistException e) {
//				// TODO Auto-generated catch block
//				throw e;
//			}
//		}
		
	}
	
	public void delete2(String idcard) throws StudentNotExistException{
		Document document ;
		boolean isDelete = false;
		try {
			document = XmlUtils.getDocument();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException();
		}
		//	nodeList是得到所有的name标签的集合
		//	nodeList.item是从name标签的集合中取出第几个
		//	nodeList.item.getTextContent拿到此节点的文本内容<name>文本内容</name>
		NodeList nodeList = document.getElementsByTagName("name");
		for(int i = 0, len = nodeList.getLength(); i < len; i++){
			if(nodeList.item(i).getTextContent().equals(idcard)){
				nodeList.item(i).getParentNode().getParentNode().removeChild(nodeList.item(i).getParentNode());
				isDelete = true;
			}
		}
		
		if(isDelete){
			try {
				XmlUtils.write2Xml(document);
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
				throw new RuntimeException(e);
			}
		}else{
			try {
				throw new StudentNotExistException(idcard + "不存在");
			} catch (StudentNotExistException e) {
				// TODO Auto-generated catch block
				throw e;
			}
		}
		
	}
	
	//	按考试编号查询学生
	public Student find(String examid){
		Document document ;
		try {
			document = XmlUtils.getDocument();
		} catch (Exception e) {
			e.printStackTrace();
			throw new RuntimeException();
		}
		//	nodeList.itemt().getAttributes()，无法获得指定的属性
		//	所以要用element.item().getAttributes("指定属性")
		//	记忆练习：从节点中拿到指定的子节点,的文本内容
		//	记忆练习：从节点中拿到指定的属性值
		NodeList nodeList = document.getElementsByTagName("student");
		for(int i = 0, len = nodeList.getLength(); i < len; i++){
			Element student_tag = (Element) nodeList.item(i);		
			if(student_tag.getAttribute("examid").equals(examid)){
				Student s = new Student();
				s.setExamid(examid);
				s.setGrade(Double.parseDouble(student_tag.getElementsByTagName("grade").item(0).getTextContent()));
				s.setIdcard(student_tag.getAttribute("idcard"));
				s.setLocation(student_tag.getElementsByTagName("location").item(0).getTextContent());
				s.setName(student_tag.getElementsByTagName("name").item(0).getTextContent());
				return s;
			}
			
		}
		return null;
		
	}
	
	public void update(){
		
	}
}

<?xml version="1.0" encoding="UTF-8" standalone="no"?><exam>
	<student examid="121" idcard="121">
    	<name>aa</name>
    	<location>北京</location>
    	<grade>98.0</grade>  
	</student>


<student examid2="111" idcard="333"><name>a</name><location>bj</location><grade>222.0</grade></student>
<student examid2="111" idcard="333"><name>a</name><location>bj</location><grade>222.0</grade></student>
<student examid2="111" idcard="333"><name>a</name><location>bj</location><grade>222.0</grade></student>

<student examid="111" idcard="2"><name>a</name><location>bj</location><grade>222.0</grade></student>
<student examid2="111" idcard="333"><name>a</name><location>bj</location><grade>222.0</grade></student>


</exam>

package com.lee.test;

import org.junit.Test;

import com.lee.dao.StudentDao;
import com.lee.domain.Student;
import com.lee.exception.StudentNotExistException;

public class StudentDaoTest {

	@Test
	public void addTest(){
		StudentDao dao = new StudentDao();
		Student s = new Student();
		
		String examid = "111";
		double grade = 222;
		String idcard  = "333";
		String location = "bj";
		String name = "a";
		
		s.setExamid(examid);
		s.setGrade(grade);
		s.setIdcard(idcard);
		s.setLocation(location);
		s.setName(name);
		dao.add(s);
	}
	
	@Test
	public void deleteTest() throws StudentNotExistException{
		StudentDao dao = new StudentDao();
		String idcard  = "333";

		dao.delete(idcard);
	}
	
	@Test
	public void findTest(){
		StudentDao dao = new StudentDao();
		String examid  = "1";

		Student s = dao.find(examid);
		System.out.println(s.getExamid());
	}
}