XML

1、XML An introduction to the

1. Concept ：

​ xml Is an extensible markup language .（ Extensible means that there are labels that can be customized ）

2. effect

​ To hold data , And these data are self descriptive

​ It can also be used as the configuration file of the project or module

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

3. grammar

The document statement

​ Create a xml file

<?xml version="1.0" encoding="UTF-8"?>
 The above content is for xml Statement 
version Express xml Version of 
encoding Express xml The encoding of the file itself 

Elements （ label ）

​ xml Element means from （ And includes ） Start tagging until （ And includes ） End the part of the tag

​ Can include elements other elements 、 Text or a combination of both

​ Naming rules ：

​ New names can contain letters 、 Numbers and other characters

​ Names cannot begin with numbers or punctuation

​ The name cannot be in characters “xml”（ perhaps XML、Xml） Start

​ The name cannot contain spaces

​ * As short as possible , Don't be too long. . Spaces cannot be included . There are also single labels and double labels

<book sn=“SN54174544” name=" Exorcism sword " author=“ Lin Pingzhi ” price=“9999”/>

<books><!-- books Represents multiple book information  -->
	<book sn=“SN54174544”>  <!-- book Represents a book information  sn Property represents the book serial number  -->
    	<name> A brief history of time </name> <!-- name Indicates the title of the book  -->
        <author> Hawking </author><!-- author The author  -->
        <price>75</price><!-- price It means the price  -->
    </book>
</books>

xml attribute

​ Additional information about labels can be provided , Must use “ ” Lead up . The document must have a root element （ Top level element without parent tag ） And only

<books><!-- books Represents multiple book information  -->
	<book sn=“SN54174544”>  <!-- book Represents a book information  sn Property represents the book serial number  -->
    	<name> A brief history of time </name> <!-- name Indicates the title of the book  -->
        <author> Hawking </author><!-- author The author  -->
        <price>75</price><!-- price It means the price  -->
    </book>
</books>
sn For attributes 

xml notes

<books><!-- books Represents multiple book information  -->
	<book sn=“SN54174544”>  <!-- book Represents a book information  sn Property represents the book serial number  -->
    	<name> A brief history of time </name> <!-- name Indicates the title of the book  -->
        <author> Hawking </author><!-- author The author  -->
        <price>75</price><!-- price It means the price  -->
    </book>
</books>
<!-- book Represents a book information  sn Property represents the book serial number  --> For comment    And html The comments of are the same <!-- -->

Text area （CDATA District ）

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

​ effect ： You can tell xml Parser , I CDATA The content in the text is pure text , Unwanted xml analysis

<![CDATA[<<<<<<<< sand ]]> 
<!--  Inside <<<<<<< Sand is text  -->

2、xml Introduction to parsing technology

​ have access to w3c Organization customized dom Technical analysis

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

3、dom4j Parsing Technology （ a key ）

​ 1.dom4j Use of class library （ Go to the official website to download ）

​ 2.dom4j Programming steps

​ 3. obtain document object

​ Guide pack dom4j.jar

​ Create a SAXReader Input stream , Read out xml Configuration file for , Generate document object

​ SaxReader.read(“xml Of documents url”);