3.2XML中的XPath和XML、对象之间的转换

（XPath、XMl和对象之间的转换）

1、XPath的介绍

XPath 是一门在 XML 文档中查找信息的语言。类似于数据库的SQL。

XPath 是通过元素和属性进行查找

XPath简化了Dom4j查找节点的过程
使用XPath必须导入jaxen-1.1-beta-6.jar
否则出现NoClassDefFoundError: org/jaxen/JaxenException

2、Xpath语法：

3、XPath进行信息查询的代码：

package com.test;import java.io.File;import java.util.List;import org.dom4j.Document;import org.dom4j.Element;import org.dom4j.io.SAXReader;public class TestXPath {public static void main(String[] args) {File xmlFile = new File("D:\\WorkSpace6.5\\java1603\\Eclipse\\Xml_Project\\src\\student.xml");SAXReader saxReader = new SAXReader();String xpath = "";List<Element> stuList = null;Element element = null;try {Document document = saxReader.read(xmlFile);Element root = document.getRootElement();/** * 1：通过XPath来查找节点 */// 1：查找XML所有的studentxpath = "/root/student";stuList = document.selectNodes(xpath);System.out.println(stuList.size());/** * 2：使用相对路径，从root来查询 */stuList = root.selectNodes("student");System.out.println(stuList.size());/** * 3：获取所有name为student元素对象，不考虑位置 */stuList = document.selectNodes("//student");System.out.println(stuList.size());// 2：查询sudent元素中id = 4的元素节点element = (Element) document.selectSingleNode("//student[@id='4']");System.out.println(element.attributeValue("id"));// 3：查询性别为男的元素节点stuList = document.selectNodes("/root/student[stu_sex='男']");System.out.println(stuList.size());// 4：查询名称中包含"a"的元素节点,类似like语句。stuList = document.selectNodes("/root/student[contains(stu_name,'a')]");System.out.println(stuList.size());// 4：查询名称中包含"a"的元素节点,或者年龄大于20岁stuList = document.selectNodes("/root/student[contains(stu_name,'a') or stu_age>=20]");System.out.println(stuList.size());// 4：查询名称中包含"a"的元素节点,并且年龄大于20岁stuList = document.selectNodes("/root/student[contains(stu_name,'a')][stu_age>=20]");System.out.println(stuList.size());} catch (Exception e) {e.printStackTrace();}}}

4、XMl与对象之间的转换

package com.test;import java.io.FileOutputStream;import com.bean.StudentBean;import com.thoughtworks.xstream.XStream;import com.thoughtworks.xstream.io.xml.DomDriver;import com.thoughtworks.xstream.io.xml.XmlFriendlyNameCoder;import com.thoughtworks.xstream.io.xml.XppDriver;/** * XML与Java对象之间的转换 *  * @author ctd * */public class XmlToJava {public static void main(String[] args) {XmlToJava.objectToXML();// XmlToJava.xmlToObject();}private static void objectToXML() {StudentBean student = new StudentBean();student.setStu_id(1);student.setStu_name("admin");student.setStu_sex("男");student.setStu_content("备注内容");student.setStu_age(20);/** * 将对象转为XML字符串/XML文件 *  * 1：通过字符串的拼接 *  * 2：通过X-Stream对象来进行转换，得包含xstream-1.4.5.jar *//** * 解决下划线的问题 */XStream stream = new XStream(new XppDriver(new XmlFriendlyNameCoder("_-", "_")));/** * 更改根节点的名称 */stream.alias("root", StudentBean.class);/** * 将id做为属性 */stream.aliasAttribute(StudentBean.class, "stu_id", "id");System.out.println(stream.toXML(student));/** * 生成一个文件 */try {FileOutputStream fileOutputStream = new FileOutputStream("E:\\test.xml");fileOutputStream.write("<?xml version=\"1.0\" encoding=\"UTF-8\"?>".getBytes());fileOutputStream.write("\n".getBytes());stream.toXML(student, fileOutputStream);} catch (Exception e) {e.printStackTrace();}}private static void xmlToObject() {XStream stream = new XStream(new DomDriver());stream.alias("root", StudentBean.class);stream.aliasAttribute(StudentBean.class, "stu_id", "id");StringBuffer xml = new StringBuffer();xml.append("<root id='2'>");xml.append("  <stu_name>admin</stu_name>");xml.append("  <stu_sex>男</stu_sex>");xml.append("  <stu_age>20</stu_age>");xml.append("  <stu_content>备注内容</stu_content>");xml.append("</root>");StudentBean studentBean = (StudentBean) stream.fromXML(xml.toString());System.out.println(studentBean.getStu_id() + "\t"+ studentBean.getStu_name());}}

studentBean.java

package com.bean;public class StudentBean {private int stu_id;private String stu_name;private String stu_sex;private int stu_age;private String stu_content;public int getStu_id() {return stu_id;}public void setStu_id(int stu_id) {this.stu_id = stu_id;}public String getStu_name() {return stu_name;}public void setStu_name(String stu_name) {this.stu_name = stu_name;}public String getStu_sex() {return stu_sex;}public void setStu_sex(String stu_sex) {this.stu_sex = stu_sex;}public int getStu_age() {return stu_age;}public void setStu_age(int stu_age) {this.stu_age = stu_age;}public String getStu_content() {return stu_content;}public void setStu_content(String stu_content) {this.stu_content = stu_content;}}