Technical point 5: XML language

xml

One 、XML brief introduction

What is? xml？

　　xml It's an extensible markup language .

xml The role of ？

　　1. To hold data , And the data are self descriptive ;

　　2. It can be used as a configuration file for a project or module ;

　　3. It can also be used as a network transmission data format （ Now in order to JSON Mainly ）.

Two 、xml grammar

1、 The document statement

　　 Let's create a simple XML file , Used to describe book information .

① Create a XML file

 

  Input file name ：

 

 ②books.xml Files store books and information .（ Books have id attribute It means only identification , Title , There are authors , Price information ）

<?xml version="1.0" encoding="utf-8" ?>
<!--xml Statement of ,version： edition   encoding： code -->
<books>
    <book id="sn7384378"><!-- book Used to describe a book ,id Property describes the number of the book  -->
        <name>java Programming idea </name>
        <author> Xiao Zhang </author>
        <price>9.9</price>
    </book>
    <book id="sn3785738">
        <name> Journey to the west </name>
        <author> Wu chengen </author>
        <price>99</price>
    </book>
</books>

You can view the document in the browser ：

 

 

2、xml notes

　　xml And HTML It's the same ：<!-- The comment -->

3、 Elements （ label ）

What is? xml Elements ?

　　xml The element refers to the part from the start tag to the end tag . Elements can contain other elements 、 Text or a mixture of the two . Elements can also have attributes .

XML Naming rules ：

　　① Name can contain letters 、 Numbers and other characters ;

　　② Names cannot begin with Numbers or punctuation marks ;

　　③ The name cannot contain spaces ;

xml The elements in （ label ） also Divide into Single label and double label ：

 Single label ：
    < Tag name   Property name =" Property value " />

 Double label ：
    < Tag name   Property name =" Property value ">
         Encapsulated data 
    </ Tag name >

 

 

4、xml attribute

　　xml Tag properties and html The tag properties of are very similar , Attributes can provide additional information about the element .

Attributes can be written on the label ：

　　 Multiple attributes can be written on a label . The value of each property must use quotes Lead up .

5、 Rule of grammar

　　① be-all xml label , Whether single label or double label , Must be closed .

　　②xml Tags are case sensitive .

　　③xml Tags must be nested correctly .

　　④XML The document must have a root element

　　　　 The root element is the top element ,

　　　　 Elements without parent tags , It's called the top element .

　　　　 The root element is a top-level element without a parent tag , And it's the only one .

 

 　　⑤xml Property values of must be quoted .

　　⑥xml Special character in ：

　　

　　 ⑦ Text area （CDATA District ） 

　　　　CDATA Grammar can tell xml Parser , I CDATA The text in , It's just plain text , Unwanted xml Syntax parsing .

　　　　CDATA Format ：

　　　　　　 <![CDATA[ Here you can display the characters you entered as they are , No resolution xml ]]>

 

 

3、 ... and 、xml Introduction to parsing technology

xml Extensible markup language .

Whether it's html The file or xml Files they're all markup documents , You can use w3c Made by the organization dom Technology to analyze .

document Object represents the entire document （ It can be html file , It can also be xml file ）

 

  Four 、dom4j Parsing Technology （ a key *****）

　　 because dom4j It is not sun Company technology , And technology that belongs to a third party company , We need to use dom4j You need to get to dom4j Download from the official website dom4j

Of jar package . 

1、Dom4j Use of class library

 

  After decompressing ：

 

 

2、dom4j Introduction to the catalogue

docs yes writing files Objective record

 

 

How to check Dom4j Documents

 

 

Dom4j Quick start

 

 

lib Catalog

 

 src Directory is dom4j Source directory

 

 

3、dom4j Programming steps ：

 

 

4、 obtain document object

　　 Create a lib Catalog , add to dom4j Of jar package , And add it to the classpath ：

 

　　 Prepare the books.xml file （ This file is in src Next ）：

<?xml version="1.0" encoding="utf-8" ?>
<!--xml Statement of ,version： edition   encoding： code -->
<books>
    <book id="sn7384378"><!-- book Used to describe a book ,id Property describes the number of the book  -->
        <name>java Programming idea </name>
        <author> Xiao Zhang </author>
        <price>9.9</price>
    </book>
    <book id="sn3785738">
        <name> Journey to the west </name>
        <author> Wu chengen </author>
        <price>99</price>
    </book>
</books>

　　 obtain document object ：

public class dom4jTest {
    @Test
    public void getDocument() throws DocumentException {
        //1. Create a SAXReader object 
        SAXReader reader = new SAXReader();
        //2. This object is used to read xml file , return Document
        Document document = reader.read("src/books.xml");
        //3. Print , See if it was created successfully 
        System.out.println(document);
    }
}

The effect is as follows ：

 

 

5、 Traverse label Get the content of all tags （***** a key ）

 Book.java file ：

public class Book {
    private String id;
    private String name;
    private String author;
    private Double price;

    public Book() {
    }

    public Book(String id, String name, String author, Double price) {
        this.id = id;
        this.name = name;
        this.author = author;
        this.price = price;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", author='" + author + '\'' +
                ", price=" + price +
                '}';
    }
}

dom4j Parse test class ：

public class dom4jTest {
    @Test
    public void readXml() throws DocumentException {
        //1. Create a SAXReader object 
        SAXReader reader = new SAXReader();
        Document document = reader.read("src/books.xml");
        //2. adopt document object , Get xml The root element object of 
        Element rootElement = document.getRootElement();
        // Print test 
//        System.out.println(rootElement.asXML());
        //3. Through the root element object , Get all book A collection of tag objects 
        List<Element> books = rootElement.elements("book");
        //4. Traverse books, Get every book object 
        for (Element book : books){
            // Get book The attribute value 
            String sn = book.attributeValue("sn");
            // Get book Below name Content in the element 
            Element name = book.element("name");
            String nameText = name.getText();
            // Get book Below author Content in the element 
            Element author = book.element("author");
            String authorText = author.getText();
            // Get book Below price Content in the element 
            Element price = book.element("price");
            String priceText = price.getText();
            // Encapsulate the acquired data into a Book object 
            Book b = new Book(sn, nameText, authorText, Double.parseDouble(priceText));
            System.out.println(b);
        }
    }
}

The effect is as follows ：