廖雪峰Java14Java操作XML和JSON-1XML-2DOM

XML是一种数据表示形式。

  • 可以描述非常复杂的数据数据结构
  • 用于传输和传输数据

DOM:Document Object Model
DOM模型就是把XML文档作为一个树形结构,从根结点开始,每个节点都可以包含任意个字节点。

用Java解析XML时,

  • Document代表整个XML文档
  • Element表示元素
  • Attribute:属性
  • Comment表示注释

Java DOM核心API:

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(XML_URL);
        Element root = doc.getDocumentElement(); //获取根结点的元素
        //从根结点document出发,可以便利所有的子节点,获取所有元素、属性、文本、数据、注释。每个Node都有自己的type,根据type来区分一个Node到底是元素,还是属性,还是文本。

遍历XML文件

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

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

public class DomSample {
    static final  String XML_URL = "http://rss.sina.com.cn/tech/internet/home28.xml";
    public static void main(String[] args) throws Exception{
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(XML_URL);
        printNode(doc,0);
    }
    static void printNode(Node n, int indent){
        for(int i=0;i<indent;i++){
            System.out.print(' ');
        }
        switch (n.getNodeType()){
            case Node.DOCUMENT_NODE://根节点
                System.out.println("Document:"+n.getNodeName());
                break;
            case Node.ELEMENT_NODE: //元素
                System.out.println("Element:"+n.getNodeName());
                break;
            case Node.TEXT_NODE: //字符
                System.out.println("Text:"+n.getNodeName()+"="+n.getNodeValue());
                break;
            case Node.ATTRIBUTE_NODE: //属性
                System.out.println("Attr:"+n.getNodeName()+"="+n.getNodeValue());
                break;
            case Node.CDATA_SECTION_NODE: //CDATA
                System.out.println("CDATA:"+n.getNodeName()+"="+n.getNodeValue());
                break;
            case Node.COMMENT_NODE: //注释
                System.out.println("Commment:"+n.getNodeName()+"="+n.getNodeValue());
                break;
            default:
                System.out.println("NodeType:"+n.getNodeType()+",NodeName:"+n.getNodeName());
        }
        for(Node child=n.getFirstChild();child != null;child=child.getNextSibling()){
            printNode(child, indent+1);
        }
    }
}
<?xml version="1.0" encoding="utf-8" ?>
<bookstore>

    <book id="1" date="08/08/2008">
        <name>冰与火之歌</name>
        <author>乔治马丁</author>
        <year>2014</year>
        <price>89</price>
    </book>

    <book id="2">
        <name>安徒生童话</name>
        <year>2004</year>
        <price>77</price>
        <language>English</language>
    </book>
</bookstore>
    public static void main(String[] args) throws Exception{
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse("./src/main/resources/test.xml");
        //通过元素名称解析得到所有子节点的集合
        NodeList books = doc.getElementsByTagName("book");
        for(int i=0;i<books.getLength();i++){
            Node book = books.item(i);
            NamedNodeMap mapOfAttr = book.getAttributes();
            //打印节点book的属性值
            for(int j=0;j<mapOfAttr.getLength();j++){
                Node nodeOfAttr = mapOfAttr.item(j);
                System.out.println(nodeOfAttr.getNodeName()+"\t"+nodeOfAttr.getNodeValue());
            }
            //获取节点book的子节点,并打印子节点名称和节点值
            NodeList childsOfBook = book.getChildNodes();
            for(int l=0;l<childsOfBook.getLength();l++){
                if(l%2 != 0){//节点共有9个,偶数节点没有内容
                    Node childOfbook = childsOfBook.item(l);
                    System.out.print(childOfbook.getNodeName()+"\t=\t");
                    //闭合标签内部被认为是子节点
                    Node grandchildNodeBook = childOfbook.getFirstChild();
                    System.out.println(grandchildNodeBook.getNodeValue());
                }
            }
        }
    }
    public static void main(String[] args) throws Exception{
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse("./src/main/resources/test.xml");
        NodeList books2 = doc.getElementsByTagName("book");
        Node book = books.item(0);
        NodeList childsOfBook = book.getChildNodes();
        for(int l=0;l<childsOfBook.getLength();l++){
            System.out.println("全部子节点"+ childsOfBook.item(l).getNodeName());
        }
    }

总结:

Java DOM API:

  • 将XML解析为DOM
  • 可在内存中完整表示XML数据结构
  • 解析速度慢,内存占用大

学习链接https://blog.csdn.net/root_dream/article/details/61195793

posted on 2019-08-19 19:58  singleSpace  阅读(150)  评论(0编辑  收藏  举报