Dom4j parsing XML, XPath retrieving XML

XML Grammar explanation

summary

Two ways of parsing
1.SAX analysis
2.DOM analysis

Dom Common parsing tools

DOM Parsing document object model

Dom4J analysis XML file

Dom4J Official website ： https://dom4j.github.io/

Implementation steps

1. download Dom4j frame ;
2. Create a folder in the project ：lib;
3. take dom4j-2.1.1.jar File copy to lib Folder ;
4. stay jar Right click on the file , choice Add as Library -> Click on OK;
5. Use of import package in class ;

Constructors 、 Method

Dom4J The analytic thought of the theory
Get document object Document, Get the element object and content from it .

SAXReader class

Constructors	explain
public SAXReader()	establish Dom4J Parser object for
Document read(String url)	load XML The file becomes Document object

Document class

Method	explain
Element getRootElement()	Get the root element object
List<Element> elements()	Get all child elements under the current element
List<Element> elements(String name)	Get the child element with the specified name under the current element and return the collection
Element element(String name)	Get the child element with the specified name under the current element , If there are many people with the same name, return the first
String getName()	Get the element name
String attributeValue(String name)	Get the attribute value directly through the attribute name
String elementText( Child element name )	Get the text of the child element with the specified name
String getText()	Get the text

Code example

Dom4JDemo1.java

public class Dom4JDemo1 {
    
    @Test
    public void parseXMLData() throws Exception {
    
        // 1、 Create a Dom4j Parser object for , Represents the whole dom4j frame 
        SAXReader saxReader = new SAXReader();

        // 2、 hold XML The file is loaded into memory and becomes a Document Document object 
        // Document document = saxReader.read(new File("xml-app\\src\\Contacts.xml")); //  You need to locate by module name 
        // Document document = saxReader.read(new FileInputStream("xml-app\\src\\Contacts.xml"));

        //  Be careful : getResourceAsStream Medium / Is directly to src Find the file under 
        InputStream is = Dom4JDemo1.class.getResourceAsStream("/Contacts.xml");
        Document document = saxReader.read(is);

        // 3、 Get the root element object 
        Element root = document.getRootElement();
        System.out.println(root.getName());

        // 4、 Take all child element objects under the root element ( Class A )
        // List<Element> sonEles = root.elements();
        List<Element> sonEles =  root.elements("contact");
        for (Element sonEle : sonEles) {
    
            System.out.println(sonEle.getName());
        }

        //  Take a child element 
        Element userEle = root.element("user");
        System.out.println(userEle.getName());

        //  The first child element object is extracted by default  (Java Language .)
        Element contact = root.element("contact");
        //  Get sub element text 
        System.out.println(contact.elementText("name"));
        //  Remove space before and after 
        System.out.println(contact.elementTextTrim("name"));
        //  Get the sub element object under the current element 
        Element email = contact.element("email");
        System.out.println(email.getText());
        //  Remove space before and after 
        System.out.println(email.getTextTrim());

        //  Get the attribute value according to the element 
        Attribute idAttr = contact.attribute("id");
        System.out.println(idAttr.getName() + "-->" + idAttr.getValue());
        //  Extract attribute values directly 
        System.out.println(contact.attributeValue("id"));
        System.out.println(contact.attributeValue("vip"));
    }
}

Contacts.xml

<?xml version="1.0" encoding="UTF-8"?>
<contactList>
    <contact id="1" vip="true">
        <name>    Pan Jinlian   </name>
        <gender> Woman </gender>
        <email>[email protected]</email>
    </contact>
    <contact id="2" vip="false">
        <name> Wusong </name>
        <gender> male </gender>
        <email>[email protected]</email>
    </contact>
    <contact id="3" vip="false">
        <name> Wu Dawang </name>
        <gender> male </gender>
        <email>[email protected]</email>
    </contact>
    <user>
    </user>
</contactList>

XML Search Technology ：Xpath

XPath Introduce

XPath Use path expressions to locate XML Element node or attribute node in the document ,Xpath Technology is more suitable for information retrieval .

Usage flow

1. Import jar package (dom4j and jaxen-1.1.2.jar),Xpath Technology depends on Dom4j technology ;
2. adopt dom4j Of SAXReader obtain Document object ;
3. utilize XPath Provided API, combination XPath Complete the selection with the syntax of XML Parse the document element node ;

Method	explain
Node selectSingleNode(" expression ")	Get the unique element that matches the expression
List<Node> selectNodes(" expression ")	Get a collection of elements that match the expression

Xpath Search method of

1. Absolute path

/ Root element / Subelement / Sun element
Use the absolute path to get the list of search nodes layer by layer from the root node and return information .
Start with the root element , Look down one level at a time , You can't cross levels .

2. Relative paths

./ Subelement / Sun element
First get the root node , Then the relative path is used to obtain the child nodes of the next level node and return information .
Start with the current element , Look down one level at a time , You can't cross levels .

3. Full text search

Direct full-text search of all specified elements and return .

4. Property search

Search for properties in full text , Or elements with attributes .

Code example

XPathDemo.java

public class XPathDemo {
    
    /** 1. Absolute path : / Root element / Subelement / Subelement . */
    @Test
    public void parse01() throws Exception {
    
        // a、 Create parser object 
        SAXReader saxReader = new SAXReader();
        // b、 hold XML Load as Document Document object 
        Document document =
                saxReader.read(XPathDemo.class.getResourceAsStream("/Contacts2.xml"));
        // c、 Retrieve all names 
        List<Node> nameNodes = document.selectNodes("/contactList/contact/name");
        for (Node nameNode : nameNodes) {
    
            Element  nameEle = (Element) nameNode;
            System.out.println(nameEle.getTextTrim());
        }
    }

    /** 2. Relative paths ： ./ Subelement / Subelement . (. Represents the current element ) */
    @Test
    public void parse02() throws Exception {
    
        // a、 Create parser object 
        SAXReader saxReader = new SAXReader();
        // b、 hold XML Load as Document Document object 
        Document document =
                saxReader.read(XPathDemo.class.getResourceAsStream("/Contacts2.xml"));
        Element root = document.getRootElement();
        // c、 Retrieve all names 
        List<Node> nameNodes = root.selectNodes("./contact/name");
        for (Node nameNode : nameNodes) {
    
            Element  nameEle = (Element) nameNode;
            System.out.println(nameEle.getTextTrim());
        }
    }

    /** 3. Full text search ： // Elements   Find this element in the full text  // Elements 1/ Elements 2  Find elements in the full text 1 The following primary elements 2 // Elements 1// Elements 2  Find elements in the full text 1 All the elements below 2 */
    @Test
    public void parse03() throws Exception {
    
        // a、 Create parser object 
        SAXReader saxReader = new SAXReader();
        // b、 hold XML Load as Document Document object 
        Document document =
                saxReader.read(XPathDemo.class.getResourceAsStream("/Contacts2.xml"));
        // c、 Retrieving data 
        //List<Node> nameNodes = document.selectNodes("//name");
        // List<Node> nameNodes = document.selectNodes("//contact/name");
        List<Node> nameNodes = document.selectNodes("//contact//name");
        for (Node nameNode : nameNodes) {
    
            Element  nameEle = (Element) nameNode;
            System.out.println(nameEle.getTextTrim());
        }
    }

    /** 4. Property search . //@ The attribute name   Retrieve property objects in full text . // Elements [@ The attribute name ]  Retrieve the element object containing this attribute in full text . // Elements [@ The attribute name = value ]  Search the element object containing the attribute and the attribute value is the value in the full text . */
    @Test
    public void parse04() throws Exception {
    
        // a、 Create parser object 
        SAXReader saxReader = new SAXReader();
        // b、 hold XML Load as Document Document object 
        Document document =
                saxReader.read(XPathDemo.class.getResourceAsStream("/Contacts2.xml"));
        // c、 Retrieving data 
        List<Node> nodes = document.selectNodes("//@id");
        for (Node node : nodes) {
    
            Attribute attr = (Attribute) node;
            System.out.println(attr.getName() + "===>" + attr.getValue());
        }

        //  Inquire about name Elements （ contain id Attribute ）
// Node node = document.selectSingleNode("//name[@id]");
        Node node = document.selectSingleNode("//name[@id=888]");
        Element ele = (Element) node;
        System.out.println(ele.getTextTrim());
    }
}

Contacts2.xml

<?xml version="1.0" encoding="UTF-8"?>
<contactList>
    <contact id="1" vip="true">
        <name>    Pan Jinlian   </name>
        <gender> Woman </gender>
        <email>[email protected]</email>
    </contact>
    <contact id="2" vip="false">
        <name> Wusong </name>
        <gender> male </gender>
        <email>[email protected]</email>
    </contact>
    <contact id="3" vip="false">
        <name> Wu Dawang </name>
        <gender> male </gender>
        <email>[email protected]</email>
    </contact>
    <user>
        <contact>
            <info>
                <name id="888"> I'm XiMenqing </name>
            </info>
         </contact>
    </user>
</contactList>