XML语言学习5--DOM4J解析+xpath

Dom4j是一个简单、灵活的开放源代码的库。Dom4j是由早期开发JDOM的人分离出来而后独立开发的。与JDOM不同的是，dom4j使用接口和抽象基类，虽然Dom4j的API相对要复杂一些，但它提供了比JDOM更好的灵活性。 
Dom4j是一个非常优秀的Java XML API，具有性能优异、功能强大和极易使用的特点。现在很多软件采用的Dom4j，例如Hibernate，包括sun公司自己的JAXM也用了Dom4j。

使用Dom4j开发，需下载dom4j相应的jar文件。

开放源代码使用技巧：docs->index.html->quick start

<span style="white-space:pre"></span>SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element root = document.getRootElement();

查询标签：

    @Test    public void read() throws DocumentException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element root = document.getRootElement();        List list = root.elements("书");        Element book = (Element)list.get(1);        Element book_name = book.element("书名");        System.out.println(book_name.getText());    }

查询属性：

//    <书 name="yyyyyyy">    @Test    public void readAttribute() throws DocumentException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element root = document.getRootElement();        String value = root.element("书").attributeValue("name");        System.out.println(value);    }

增加节点：

//    增加售价节点    @Test    public void add() throws DocumentException, IOException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element price = DocumentHelper.createElement("售价");        price.setText("19元");        document.getRootElement().element("书").add(price);        OutputFormat format = OutputFormat.createPrettyPrint();        XMLWriter writer = new XMLWriter(new FileOutputStream("src/book1.xml"),format);        writer.write(document);        writer.close();    }

修改：

//    修改： <售价>109</售价>    @Test    public void update() throws IOException, DocumentException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element price = (Element) document.getRootElement().element("书").elements("售价").get(1);        price.setText("209");        OutputFormat format = OutputFormat.createPrettyPrint();        XMLWriter writer = new XMLWriter(new FileOutputStream("src/book1.xml"),format);        writer.write(document);        writer.close();    }

删除：

//   删除节点<售价>109</售价>    @Test    public void delete() throws DocumentException, IOException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element price = (Element) document.getRootElement().element("书").elements("售价").get(0);        price.getParent().remove(price);        OutputFormat format = OutputFormat.createPrettyPrint();        XMLWriter writer = new XMLWriter(new FileOutputStream("src/book1.xml"),format);        writer.write(document);        writer.close();    }

指定节点的插入：

 //    向指定位置增加售价节点    @Test    public void add2() throws DocumentException, IOException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element price = DocumentHelper.createElement("售价");        price.setText("19元");        List list = document.getRootElement().element("书").elements();        list.add(1,price);        OutputFormat format = OutputFormat.createPrettyPrint();        XMLWriter writer = new XMLWriter(new FileOutputStream("src/book1.xml"),format);        writer.write(document);        writer.close();    }

xPath的使用：

查找某一节点：

    @Test    public void findWithXpath() throws DocumentException {        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/book1.xml"));        Element name = (Element) document.selectNodes("//书名").get(1);        System.out.println(name.getText());    }

实例：

 @Test    public void findUsers() throws DocumentException, IOException {       /* BufferedReader br = new BufferedReader(new InputStreamReader(System.in));        System.out.print("请输入用户名：");        String username = br.readLine();        System.out.print("请输入密码：");        String password = br.readLine();*/        String username = "aaa";        String password = "123";        SAXReader reader = new SAXReader();        Document document = reader.read(new File("src/users.xml"));        Element e = (Element) document.selectSingleNode("//user[@username='" + username + "' and @password='" + password + "']");        if (e != null){            System.out.println("登陆成功!");        }else{            System.out.println("用户不存在或密码错误！");        }