XML

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Concept

1. Concept ： Extensible Marhup Language Extensible markup language
* Scalable ： The tags are all custom .
2. function ：
* Store the data
* 1. The configuration file
* 2. To transmit in a network
3.xml And html The difference between ：
1.xml The tags are all custom ,html Labels are predefined .
2.xml The grammar is strict ,html Loose grammar
3.xml The data of village school is ,html It's a way to show data

grammar

*  Basic grammar ：
	1. xml The suffix of the document .xml
	2. xml The first line must be defined as a document declaration 
	3. xml There is and only one root tag in the document 
	4.  The attribute value must be in quotation marks （ Single and double ） Lead up 
	5.  Label must be closed correctly （ Double label ）
	6. xml Label names are case sensitive 
*  Quick start ：
	 for example ： <?xml version = '1.0' ?>
		<users>
			<user id='1'>
                <name>zhangsan</name>
                <age>23</age>
                <gender>male</gender>
             </user>
             <user id='2'>
                <name>lisi</name>
                <age>24</age>
                <gender>female</gender>
             </user>
		</users>
*  Part of the ：
	1. The document statement 
		1. Format ：<?xml  Property list  ?> 
		2. Property list ：
			*version： Version number 
			*encoding： Encoding mode . Tells the parsing engine what character set the current document uses , The default value is ：ISO-8859-1
			*standalone： Is it independent 
				* Cancel ：
					*yes： Don't rely on other files 
					*no:  Rely on other files 
	2. Instructions （ understand ）： Combine css Of 
		* <?xml-stylesheet type="text/css" href="a.css" ?>
	3. label : Label name custom 
		* The rules ：
			*  Names can contain letters 、 Numbers and other characters .
			*  The name cannot start with a numeric punctuation mark 
			*  The name cannot be in letters xml（ perhaps XML、Xml wait ） Start 
			*  The name cannot contain spaces 
	4. attribute ：
		id Attribute is the only .
	5. Text ：
		CDATA District ： The data in this area will be displayed as is 
			* <![CDATA[  data  ]]>
* constraint ： Regulations xml Rules for writing documents 
	* As users of the framework （ The programmer ）：
		1. In the xml Constraint document is introduced in 
		2. Be able to simply read and understand the document 
	* classification ：
		1.DTD: A simple constraint technique 
		2.Schema： A complex constraint technique 
	*DTD:
		* introduce dtd Document to xml In the document 
			* Inside dtd： Define the constraint rules in xml In the document （ understand ）
			* external dtd： Define the rules of constraint in the external dtd in 
				* Local ：<!DOCTYPE  Root sign  SYSTEM "dtd The location of the file “>
				* The Internet ：<!DOCTYPE  Root sign  PUBLIC “dtd File name ” “dtd The location of the file  URL">

analysis ：

• operation xml file , Read the data in the document into memory

  operation xml file ：

  1. analysis （ Read ）： Read the data in the document into memory
  2. write in ： Save the data in memory to xml In the document . Persistent storage .

  analysis xml The way ：

  1.DOM: Load markup language documents into memory at one time , Form a... In memory dom Trees
  * advantage ： It is easy to operate , You can do CRUD All operations
  * shortcoming ： Occupy memory
  2.SAX: Read line by line , Event driven .
  * advantage ： Do not occupy memory
  * shortcoming ： Can only read , You can't add, delete, or modify

  xml Common parsers ：

  1.JAXP:sun Company supplied parsers , Support dom and sax Two thoughts （ understand ）
  2.DOM4J: A very good parser
  3.Jsoup：jsoup Is a Java Of HTML Parser , Can directly parse a URL Address 、HTML Text content . It provides a very labor-saving API, It can be done by DOM,CSS And similar to jQuery To extract and manipulate data .
  4.PULL： The built-in parser of Android operating system ,sax The way of .

  Jsoup

  jsoup Is a Java Of HTML Parser , Can directly parse a URL Address 、HTML Text content . It provides a very labor-saving API, It can be done by DOM,CSS And similar to jQuery To extract and manipulate data .

Quick start ：

  * step ：
  	1. Import jar package 
  	2. obtain Document object 
  	3. Get the corresponding label 
  	4. get data 
  * Code ：
     // obtain xml The path of 
      String path =JsoupDemo1.class.getClassLoader().getResource("student.xml").getPath();
      // obtain document file , according to xml Document access 
      Document parse = Jsoup.parse(new File(path), "utf-8");
      //3. Get element object 
      Elements name = parse.getElementsByTag("name");
      System.out.println(name.size());

Use of objects ：

1.Jsoup： Tool class , Can be parsed html perhaps xml file , return Document
*parse： Can be parsed html perhaps xml file , return Document

            * parse （File in, String charsetName）
            * parse（String html）： analysis xml or html character string .
            * parse(URL url,int timeoutMillis): Get the specified... Through the network path html or xml Document object for .

2.Document： Document object , Represents... In memory dom Trees

​ obtain Element object

    getElementsById("id")： according to id Get the collection of label elements .

    getElementsByTag("name")： Get the collection of tag elements according to the tag name .

    getElementsByAttribute（String key）： Get the element object according to the attribute name .

    getElementsByAttributeValue（String key,String value): Get the element object set according to the corresponding attribute name and attribute value .

3.Elements： Elements Element A collection of objects . Can be viewed as ArrayList To use
4.Element： Element object

1. Get child element object                  											
      1. getElementById（String id）： according to id Property value gets unique element object .           
      2. getElementsByTag("name")： Get the collection of tag elements according to the tag name .
      3. getElementsByAttribute（String key）： Get the element object according to the attribute name .
      4.  getElementsByAttributeValue（String key,String value): Get the element object set according to the corresponding attribute name and attribute value .
2. Get attribute value 
 	 1.String attr（String key）: Get the property value according to the property name .
3. Get text content .                                                                     	
 	 1.String text（）： Get text content 
 	 2.String html（）： Get all the contents of the label body （ Including the string content of the sub tag ）

5.Node： Node object
1. yes Document and Element Parent class of

Quick query

1.selector： Selectors 

	*  Method used ：Elements  select（String cssQuery）
		 grammar ：  Reference resources Selector Syntax defined in class 
2.XPath：XPath, That is to say XML Path to the language （XMLPathLanguage）, It's a way to determine XML The language of a part of a document 
	* Use Jsoup Of Xpath Need extra import jar package 
	*  Inquire about w3cshool Reference manual , Use xpath The syntax of complete query