初识XML

XML

XML概述

使用XML文件,可以保存复杂的数据,数据结构清晰(树状结构)

传输数据是一种通用的数据格式
传递数据,作为配置文件存在

XML语法

版本
<?xml version="1.0"?>

用encoding属性说明文档所使用的字符编码，默认为UTF-8。保存在磁盘上的文件编码要与声明的编码一致。
<?xml version="1.0" encoding="UTF-8"?>

用standalone属性说明文档是否独立，即是否依赖其他文档。
<?xml version="1.0" standalone="yes"?>

标签的属性,描述该标签
<linkman 属性名="属性值">

<?xml version="1.0" encoding="UTF-8"?>
<contacts> 
    <person id="1">
            <name>蔡徐坤</name>
            <address>荷兰</address>
            <email>kk@nmsl</email>
            <age>17</age>
        </person>
        <person id="2">
            <name>孙笑川</name>
            <address>日本</address>
            <email>cc@nmsl</email>
            <age>18</age>
        </person>
</contacts>

DOM解析(Document Object Model)

文档对象模型,可以将xml的操作当做是操作对象

特点:

在加载XML文档的时候,会一次性把所有的信息加载到内存中(DOM树)
使用document这一对象来描述,剩下的操作都是操作内存中的对象

缺点:

如果XML文档内容比较多,文件比较大,一加载到内存中会导致,内存溢出

注意:

1.使用DOM解析,导入的类都是在org.w3c.dom包中.如果发现让你强转.意识到可能导错包了.
2.在XML中,一切皆节点

####获取Document对象

三个类

Document
DocumentBuilder
DocumentBuilderFactory

newDocumentBuilder:单例设计模式,需要通过自身的newInstance方法,获取一个新的实例

DocumentBuilder:需要通过newDocumentBuilder的实例中的newDocumentBuilder获取对象,该类重写了parse方法和newDocument方法

Document:接口,不能创建对象.抽象的parse方法和newDocument方法

package me.cscar.DOM.object;

import org.junit.Test;
import org.w3c.dom.Document;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.File;
import java.io.InputStream;

public class GetDOMObject {
    @Test
    public void getObject() throws Exception {
        File file = new File("/Users/cscar/IdeaProjects/wolfCode/day03/resource/MyXML.xml");

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();

        Document doc = db.newDocument();

        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("MyXML.xml");
        Document doc1 = db.parse(is);

        //Document doc = db.parse(file);

        System.out.println(doc.equals(doc1));
    }
}

####常用API(增删改查)
常用的API:

Document对象:
    Element getDocumentElement(): 获取根节点.
    Element getElementById(String elementId) :根据唯一ID获取节点.
Element对象:
    NodeList getElementsByTagName(String name):根据标签名获取到标签列表.
    String getAttribute(String name) :根据属性名,获取属性值
    void setAttribute(String name, String value) :设置属性名和属性值.
Node 对象:
    String getTextContent(): 返回当前节点的文本内容.
    void setTextContent(String value): 设置文本内容.

ADD

package me.cscar.DOM.frequently;

import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;

public class Add {
    @Test
    public void useAdd() throws Exception {
        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("MyXML.xml");
        //创建document对象
        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);
        //获取根节点
        Element element = doc.getDocumentElement();
        //创建节点
        Element person = doc.createElement("person");
        person.setAttribute("id", "4");

        Element name = doc.createElement("name");
        Element email = doc.createElement("email");
        Element address = doc.createElement("address");
        Element age = doc.createElement("age");

        //创建层级关系
        element.appendChild(person);

        person.appendChild(name);
        person.appendChild(email);
        person.appendChild(address);
        person.appendChild(age);

        //给节点设置数据
        name.setTextContent("蛤蛤");
        email.setTextContent("haha@china.com");
        address.setTextContent("中国");
        age.setTextContent("90");

        SynchroFile.synchor(doc);

    }
}

REMOVE

package me.cscar.DOM.frequently;

import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;

/**
 * 删除操作
 */
public class Remove {
    @Test
    public void useRemove() throws Exception {
        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("MyXML.xml");

        //获取document对象
        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);

        //获取根节点
        Element de = doc.getDocumentElement();

        //person标签
        NodeList person = de.getElementsByTagName("person");

        //获取第三个人的标签
        Element p3 = (Element) person.item(2);
        System.out.println(p3.getAttribute("id"));

        p3.getParentNode().removeChild(p3);

        //同步操作,把修改的document对象写入

        SynchroFile.synchor(doc);

    }
}

QUERY

package me.cscar.DOM.frequently;

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

import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;

/**
 * 查询操作
 */
public class Query {
    @Test
    public void useQuery() throws Exception {
        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("MyXML.xml");

        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);

        Element de = doc.getDocumentElement();

        //第1个人的信息节点
        NodeList person = de.getElementsByTagName("person");
        System.out.println("长度是"+person.getLength());
        Element item = (Element) person.item(2);
        //获取ID编号
        //System.out.println(item.getAttribute("id"));

        //找到第1个联系人的name节点
        Element nameNode = (Element) item.getElementsByTagName("name").item(0);
        int re = item.getElementsByTagName("name").getLength();
        //System.out.println(re);
        String name = nameNode.getTextContent();
        System.out.println(name);

        //获取所有人的信息
        for (int i = 0; i < person.getLength(); i++) {
            Element item1 = (Element) person.item(i);
            String name1 = item1.getElementsByTagName("name").item(0).getTextContent();
            String email = item1.getElementsByTagName("email").item(0).getTextContent();
            String address = item1.getElementsByTagName("address").item(0).getTextContent();
            String age = item1.getElementsByTagName("age").item(0).getTextContent();
            System.out.println(name1 + '\n' + email + '\n' + address + '\n' + age);
            System.out.println("-------------");
        }
    }
}

UPDATE

package me.cscar.DOM.frequently;

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

import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;

/**
 * 修改操作
 */
public class Update {
    @Test
    public void useUpdate() throws Exception {
        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("MyXML.xml");

        //获取document对象
        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);
        //获取根标签
        Element element = doc.getDocumentElement();

        //获取第3个人信息
        Element person = (Element) element.getElementsByTagName("person").item(2);
        //获取name标签
        Element name = (Element) person.getElementsByTagName("name").item(0);

        //修改name标签
        name.setTextContent("包包");

        //调用同步方法
        SynchroFile.synchor(doc);

    }
}

同步操作

package me.cscar.DOM.frequently;

import org.w3c.dom.Document;

import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.File;
import java.io.InputStream;

/**
 * 增删改的同步操作
 * 把修改的document真正写入
 */
public class SynchroFile {

    public static void synchor(Document doc) throws Exception {

        File file = new File("/Users/cscar/IdeaProjects/wolfCode/day03/resource/MyXML.xml");

        //获取工厂对象
        TransformerFactory factory = TransformerFactory.newInstance();
        //获取转换器
        Transformer transformer = factory.newTransformer();

        //调用转换器中的方法
        Source src = new DOMSource(doc);
        Result target = new StreamResult(file);
        transformer.transform(src, target);
    }
}

创建新的XML

package me.cscar.DOM.create;

import me.cscar.DOM.frequently.SynchroFile;
import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.File;

public class Create {
    @Test
    public void CreateDoc() throws Exception {
        //File file = new File("/Users/cscar/IdeaProjects/wolfCode/day03/resource/MyXML.xml");
        File newFile = new File("/Users/cscar/IdeaProjects/wolfCode/day03/resource/MyXML_Copy.xml");

        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();

        //创建一个根节点
        Element element = doc.createElement("contacts");
        //添加根节点

        doc.appendChild(element);

        TransformerFactory factory = TransformerFactory.newInstance();
        Transformer tf = factory.newTransformer();

        Source src = new DOMSource(doc);
        Result target = new StreamResult(newFile);
        tf.transform(src, target);


    }
}

####XML约束(了解)