DOM parsing of XML file case code sentence by sentence analysis

One 、 What is? xml

        xml Is extensible markup language , Mainly used for transmission 、 Store the data , Instead of showing the data .xml When you file W3C The data transmission format recommended by the organization .

Two 、xml What is the file format

    xml The documents are mainly made up of xml Statement 、 label 、 Root element and element composition .

xml Statement ：

    <?xml  version="1.0"  encoding="UIF-8" ?>       

                 version ： Version number , Need to meet XML1.0 Format
                 encoding： Character encoding , The default is “UTF-8”

label

       <name>  " Zhang San " </name>    This is a pair of labels

        <name>  The start tag ;</name> End tag ; " Zhang San " Text content

Root element

        <people></people>  This is a pair of root elements , One xml There is only one root element in the file , The other elements are in this root element

Elements

         <name>  " Zhang San " </name> This is an element , Element is composed of child elements and character data

    Naming rules for elements ：1、 The name can contain letters 、 Numbers or other characters

                                2、 Names cannot begin with numbers or punctuation

                                3、 The name cannot be in characters xml( perhaps XML,Xml) Start

                                4、 The name cannot contain spaces   

3、 ... and 、xml File content cases

<?xml version="1.0" encoding="GB2312"?>
<PhoneInfo>
    <Brand name=" Huawei ">
        <Type>Mate30</Type>
        <Type>Hova20</Type>
        <Type>p30</Type>
    </Brand>
    <Brand name=" Apple ">
        <Type>iphone11Pro</Type>
        <Type>iphone12p</Type>
    </Brand>
</PhoneInfo>

Four 、DOM analysis xml file

       DOM Based on XML Tree structure to complete the parsing .DOM analysis xml When documenting , According to the read document , Create a tree structure stored in memory , And then through DOM The interface class operates on the tree structure ; For multiple visits xml file , Compare the consumption of resources .

       DOM It can be done to xml Read from the memory of the document , Modify and store . Collective realization , This program is explained sentence by sentence .

package cn.kgc;
import org.w3c.dom.*;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
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.FileInputStream;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
//@Author
//@Date
//@Description  demonstration DOM analysis xml file 
public class TestDome {
    Document document;
    public static void main(String[] args) {
        TestDome d = new TestDome();
        try {
            d.getDocument("resources\\ Collection information .xml");
            // One 、 Read property values 
            d.getBrands("Type","name");
            // Two 、 Read text value 
            d.getChildren("Brand");
            // 3、 ... and 、 Store data and assign values 
            d.saveXML("src\\cn\\kgc\\poeple.xml");
            // Modifying data 
            //1、 Delete 
            d.changeDele();
            d.saveXML("src\\cn\\kgc\\poeple.xml");
            //2、 Modify properties 
            d.changeName();
            d.saveXML("src\\cn\\kgc\\poeple.xml");
            //3、 add to 
            d.changeAddElement();
            d.saveXML("src\\cn\\kgc\\poeple.xml");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    // establish Document Instance object , obtain xml Document DOM Count , That is, get the root node 
    public void getDocument(String xmlPath) throws Exception {
        // establish DOM Factory instance object 
//        DocumentBuilderFactory Abstract class , No instantiated object 
//        Method ： static DocumentBuilderFactory newInstance​()  Get a new instance  DocumentBuilderFactory .
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        // from DOM The instance factory obtains DOM Parser 
//        Method ： abstract DocumentBuilder newDocumentBuilder​()  Create a new... Using the currently configured parameters DocumentBuilder example .
        DocumentBuilder buider = factory.newDocumentBuilder();
        // adopt DOM Parser parsing XML file , Get one Document object , That is to get DOM Trees 
//        Method ： Document parse​(File f)  Parse the contents of a given file into XML file , And return to a new DOM Document object .
        document = buider.parse(new FileInputStream(xmlPath));
    }
    // Get the value of the property 
    public void getBrands(String tagName , String attName) {// Print all brand names 
        // Get all tagName List of nodes 
//         Method ：  NodeList getElementsByTagName​(String tagname)  Return in document order  NodeList Of  Elements , With the given tag name , And included in the documentation 
        //  It means NodeList Represents a set , Read out the child nodes under the root node , Put it in the collection 
        NodeList breads = document.getElementsByTagName(tagName);
        for (int i = 0; i < breads.getLength(); i++) {
//             Get the label of each element 
//           Traverse all the child nodes in the collection 
//         Method ：   Node item​(int index)  Returns... In the collection  index term .
            Node brand = breads.item(i);
            // In principle, the label is Element Elements 
//            public interface Element extends Node     Element  Inherited Node Parent class , namely Node It can be transformed into Element
//             What the child node element here needs is Element type , That is, it needs to be transformed 
            Element e = (Element) brand;
            // Get the attribute value according to the attribute 
//          Method ：   String getAttribute​(String name)  Retrieve attribute values by name .
            String name = e.getAttribute(attName);
            System.out.println(name);
        }
    }
    //  Interaction between parent and child nodes , Display the text under the child node 
    public void getChildren(String tagName) {
        // Get all child nodes under the root node 
        NodeList breads = document.getElementsByTagName(tagName);
        // Traverse each child node 
        for (int i = 0; i < breads.getLength(); i++) {
            // Get the label of each node 
            Node node = breads.item(i);
            Element e = (Element) node;
            String name = e.getAttribute("name");
            System.out.println(name);
            // Take all text nodes of each child node 
//           Method ：  NodeList getChildNodes​() A NodeList Contains all child nodes of this node .
            NodeList children = node.getChildNodes();
            for (int j = 0; j < children.getLength(); j++) {
                // Each text node 
//               Method ：   Node item​(int index)  Returns... In the collection  index term .
                Node child = children.item(j);
//                if (child instanceof Element) {// Exclude empty line markers 
//                    // Convert a text node into a text file 
                if (child instanceof Element) {
                    Text text = (Text) child.getFirstChild();
                    // Output content 
                    System.out.println(text.getWholeText());
                }
            }
        }
    }

    // Storage XML data 
    public void saveXML(String path) throws Exception {
        // Create a storage factory 
        TransformerFactory factory = TransformerFactory.newInstance();
        // Create a storage factory object 
        Transformer trans = factory.newTransformer();
        // Format adjustment 
        trans.setOutputProperty(OutputKeys.INDENT , "yes");
        trans.setOutputProperty("{http://xml.apache.org/xslt}indent-amount" , "4");
        // establish DOMSource object , contain xml Information 
        DOMSource source = new DOMSource(document);
//        FileOutputStream fos = new FileOutputStream(path);
//        OutputStreamWriter osw =new OutputStreamWriter(fos,"GB2312");
        // Create a file input result stream object 
        StreamResult result = new StreamResult(new OutputStreamWriter(new FileOutputStream(path) , "GB2312"));
        // take DOMSource Object xml Information stored in people.xml in 
        trans.transform(source , result);
    }

    // Modify the text 
    public void changeDele() {
        //1、 Delete 
        Node root = document.getElementsByTagName("PhoneInfo").item(0);
        Node iphone = document.getElementsByTagName("Brand").item(1);
//       Method ：Node removeChild​(Node oldChild)  Remove... From the sub list  oldChild Indicated child nodes , And back to .
        root.removeChild(iphone);
    }
    public void changeName() {
//        2、 Change the apple attribute to iphone, At the same time, the sub text iphone12p Change it to iphone100
        Node iPhone = document.getElementsByTagName("Brand").item(0);
        Element e = (Element) iPhone;
        // Modify the apple attribute name “ Apple ” by “iphone”,
        e.setAttribute("name" , "iphone");
//        Method ： NodeList getChildNodes​() A NodeList Contains all child nodes of this node .
        NodeList nodes = e.getChildNodes();
        for (int i = 0; i < nodes.getLength(); i++) {
            Node node = nodes.item(i);
            //instanceof   To exclude empty elements, an error is reported 
            //  node instanceof Element   node A variable is Element type , It is true, Conversely false
            if (node instanceof Element) {
                Text text = (Text) node.getFirstChild();
                // Judge whether the text is "iphone12p", If yes, change to "iphone100" And exit 
                // Method ：String getWholeText​()  All the text of a logically adjacent text node  Text Return to this node , Connect in document order .
                if (text.getWholeText().equals("iphone12p")) {
                    text.setData("iphone100");
                    return;
                }
            }
        }
    }
    public void changeAddElement() {
        //3、 Add Samsung brand , Increase type Galay10.20
        Node root = document.getElementsByTagName("PhoneInfo").item(0);
//        Node iPhone = document.getElementsByTagName("Brand").item(1);
        // Create a new child node 
        Element brand = document.createElement("Brand");
        // Set the attribute of the child node to name=“ samsung ”
        brand.setAttribute("name"," samsung " );
        // Create the element to be added under the child node 
        Element type1 = document.createElement("Type");
        Element type2 = document.createElement("Type");
        // What is the text content of each element 
        Text t1 = document.createTextNode("Galaxy10");
        Text t2 = document.createTextNode("Galaxy20");
        // The nodes  newChild Add to the end of this node's list of child nodes .
//        Node appendChild​(Node newChild)  The nodes  newChild Add to the end of this node's list of child nodes .
        type1.appendChild(t1);
        type2.appendChild(t2);
        brand.appendChild(type1);
        brand.appendChild(type2);
        root.appendChild(document.createTextNode("\n"));
        root.appendChild(brand);
    }
}