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 blocke.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 blocke.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studentpublic void delete(String idcard) throws StudentNotExistException{Document document ;boolean isDelete = false;try {document = XmlUtils.getDocument();} catch (Exception e) {// TODO Auto-generated catch blocke.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 blockthrow e;} catch (Exception e) {// TODO Auto-generated catch blocke.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 blocke.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 blocke.printStackTrace();throw new RuntimeException(e);}}else{try {throw new StudentNotExistException(idcard + "不存在");} catch (StudentNotExistException e) {// TODO Auto-generated catch blockthrow 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 {@Testpublic 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);}@Testpublic void deleteTest() throws StudentNotExistException{StudentDao dao = new StudentDao();String idcard = "333";dao.delete(idcard);}@Testpublic void findTest(){StudentDao dao = new StudentDao();String examid = "1";Student s = dao.find(examid);System.out.println(s.getExamid());}}