XML Overview
Extensible Markup Language: scalable Markup Language
use:
1. Data storage, small databases, there is a certain CRUD operations feasibility
2. The data transmission network
3.JavaWEB Framework Project Profiles
The basic syntax:
1.XML file extension is .xml format
2.XML first line is the defining declaration for the current file
3.XML file has one and only one root tag
4. quoted attribute values must contain recommended double quotes
The label must be properly matched, correct and proper closing start
6.XML label within strict case-sensitive
Writing the code:
<?xml version="1.0" ?>
<users>
<user id="1">
<name>James</name>
<age>16</age>
</user>
<user id="2">
<name>JK</name>
<age>16</age>
</user>
</users>Part of the XML file
1 document declaration:
. A format:
<? Xml list of attributes? >:? <Xml version = "1.0" encoding = "utf-8">
version: The current xml file version number
encoding: coding, coding suggested here to save xml file parsing and consistent with the corresponding code set
standalone: whether to rely on other documents (understand); yes does not depend on, no dependence
2. Directive (understand)
Here you can import some css styles
3. Custom label content
rule:
a. custom tag allows the use of letters, numbers, and other punctuation
b. are not allowed to use numbers and punctuation marks the beginning, only allows the use of the English alphabet
c. xml tags are not allowed in custom labels, caps XML does not work
d. name spaces are not allowed
4. Properties
Can give the label a property, sometimes required ID attribute is unique
5. Text (Learn)
CDATA area, WYSIWYG, CDATA content area is full of show
format:
<! [CDATA [Data]]>
XML file data constraints
1.DTD
A simple way of constraint, but there are some constraints
2.Schema
A complex XML document constraint way, very strict
DTD constraints
Schema Constraint
XML parsing
XML parsing ideas:
DOM parsing : Document Object Model document object model; the entire XML document as a Document object, each node as a Element, the node has Attribute, Text or text content exists in the current node.
Dom resolution is to read the entire XML file into the computer's memory, you can make CRUD operations
Disadvantages:
It takes up a lot of memory space
For the environment:
Suitable for parsing an XML file
SAX parsing:
Read line by line, to give a certain event actions; to read single line, the line is released content, can effectively save memory space.
Disadvantages:
XML documents can not, additions or deletions to change search operation
For the environment:
Phone reading methods used when parsing an XML file
XML file parsing tools
1.JAXP：
A basic parser SUN company provides support for DOM and SAX two analytical way, but the operation is very complicated and not easy programmers to develop
2kdom4j:
DOM For Java；
A very good parser
Spring, SpringMVC ... in the framework of an integrated XML parser
3.Jsoup:
Java tool for giving complete HTML parsing, because HTML and XML files are markup language; to Jsoup a URL, page address, Java small reptiles
4.PULL
The integrated XML parsing tools on Android phones, SAX parse
Dom4j Getting Started
1. Package guide
Currently use a third-party tool, not a native JDK; to import third-party jar package
2. Set IDEA
3.Dom4j related to the method:
SAXReader (); core classes used to parse XML file
read (); XML Document object file
Document object can be used getRootElement (); method to get the current root object is an XML file
Element object methods can be used:
List elements (); all child nodes of the current node
List elements (String name); all child nodes specify the name of the current node
Element element (); obtaining a first child node of the current node under
Element element (String name); get the first child node specifies the name of the current node
Attribute getAttribute (String name); obtaining a corresponding attribute object according to the attribute Attribute name; Attribute node can use String getValue () to get the corresponding node data
String getName (); Gets the name of the current node
String getText (); Gets the current node
Dom4j Xpath parse XML file to read
XML files are saved
Process:
1. Create a Document object
2. Document object to add elements by:
addElement();
addAttribute ();
