Take you to a deeper understanding of XML

1. XML: extensible markup language version="1.0"

• ##Extensible: all tags are customized

• Function: Data storage

• Configuration file

• Data transmission

• Differences between html and xml

##HTML syntax is loose, xml syntax is strict
html is used for page display, xml is used for data Storage
All tags in Html are predefined, and all tags in xml are customized

2. xml syntax:

Document declaration
version version number fixed value 1.0
encoding specified document The default value of the code table is iso-8859-1
standalone. Specify whether the document is independent yes or no
must be written in the xml document. One line of
is written as:
Attributes

Tags in element xml document
Element names are case-sensitive
Numbers cannot begin
There must be and can only be one root element in the document
The element needs to be closed correctly

elements need to be nested correctly
element names must comply with

text
##

• Escape characters>

• The data inside CDATA will be displayed as it is
Attributes
Attribute values ​​must be enclosed in quotation marks. Both single and double quotation marks are OK

Comments

• #

• Processing instructions: Basically no need now

• 3. XML constraints

Constraints are the writing rules of xml

• Classification of constraints:

• Import xsd constraint document

• Write root tag

• Introducing the instance namespace xmlns:xsi="www.w3.org/2001/XMLSchema-instance"

• ##Introducing the namespace xsi:schemaLocation="www.itcast.cn/ xml student.xsd"

• Introducing the default namespace

• student.xsd

• student .xml

<?xml version="1.0"?>
<xsd:schema xmlns="www.itheima.cn/xml"
        xmlns:xsd="www.w3.org/2001/XMLSchema"
        targetNamespace="www.itheima.cn/xml" elementFormDefault="qualified">
    <xsd:element name="students" type="studentsType"/>
    <xsd:complexType name="studentsType">
        <xsd:sequence>
            <xsd:element name="student" type="studentType" minOccurs="0" maxOccurs="unbounded"/>
        </xsd:sequence>
    </xsd:complexType>
    <xsd:complexType name="studentType">
        <xsd:sequence>
            <xsd:element name="name" type="xsd:string"/>
            <xsd:element name="age" type="ageType" />
            <xsd:element name="sex" type="sexType" />
        </xsd:sequence>
        <xsd:attribute name="number" type="numberType" use="required"/>
    </xsd:complexType>
    <xsd:simpleType name="sexType">
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="male"/>
            <xsd:enumeration value="female"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:simpleType name="ageType">
        <xsd:restriction base="xsd:integer">
            <xsd:minInclusive value="0"/>
            <xsd:maxInclusive value="256"/>
        </xsd:restriction>
    </xsd:simpleType>
    <xsd:simpleType name="numberType">
        <xsd:restriction base="xsd:string">
            <xsd:pattern value="itheima_\d{4}"/>
        </xsd:restriction>
    </xsd:simpleType>
</xsd:schema>
<?xml version="1.0" encoding="UTF-8" ?>

<students
    xmlns="www.itheima.cn/xml"
    xsi:schemaLocation="www.itheima.cn/xml student.xsd"
    xmlns:xsi="www.w3.org/2001/XMLSchema-instance"
>
    <student number="itheima_1001">
        <name>asfd</name>
        <age>12</age>
        <sex>male</sex>
    </student>
</students>
<students
    xmlns:itheima="www.itheima.cn/xml"
    xsi:schemaLocation="www.itheima.cn/xml student.xsd"
    xmlns:xsi="www.w3.org/2001/XMLSchema-instance"
>
    <itheima:student number="itheima_1001">
        <itheima:name>asfd</itheima:name>
        <itheima:age>12</itheima:age>
        <theima:sex>male</itheima:sex>
    </itheima:student>
</itheima:students>

• Internal dtd defines dtd inside xml
• External dtd defines dtd in external file

• Student.dtd

• student.xml

• Local dtd file

• Network dtd file

<!ELEMENT students (student*) >
<!ELEMENT student (name,age,sex)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT age (#PCDATA)>
<!ELEMENT sex (#PCDATA)>
<!ATTLIST student number ID #REQUIRED> 唯一的，必须的
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE students SYSTEM  "student.dtd">
<students>
    <student number="s0001" >
        <name>zs</name>
        <age>abc</age>
        <sex>yao</sex>
    </student>
</students>

• dtd The constraints are not strict
• schema

• ##4. XML parsing

parsing XML can be done:

• If xml is used as a configuration file: read

If xml is used as a transfer file: write, read
• XML parsing ideas:

• Advantages: Does not occupy memory, fast

Disadvantages: Can only read, cannot write back
Advantages: Because a dom tree will be formed in the memory, the dom tree can be added, deleted, modified, and checked
Disadvantages: The DOM tree takes up a lot of memory and the parsing speed is slow
Document Element Text Attribute Comment
DOM: Load the document to memory, forming a DOM tree (document object), encapsulating various components of the document into some objects
SAX: read line by line, event-driven
• Commonly used parsers for xml

• define a rule

Usage method
Usage steps
XPath:

• public classTestXPath2 {
        @Test
        publicvoidtest()throwsException{
              SAXReaderread= new SAXReader();
              Documentdocument= read.read("src/Dom4jTest.xml");
              Listnodes= document.selectNodes("/bookstore//book/title");
              for(inti= 0;i< nodes.size();i++) {
                    Nodenode= (Node)nodes.get(i);
                    System.out.println(node.getText());
              }
        }
  }

• selectSingleNode()

selectNodes()
Note: To import the package jaxen...jar

• 创建解析器 SAXReader reader = new SAXReader()

• 解析xml 获得document对象 Document document = reader.read(url)

• // nodename 选取此节点。

• // / 从根节点选取。

• // // 从匹配选择的当前节点选择文档中的节点，而不考虑它们的位置。

• // .. 选取当前节点的父节点。

• // @ 选取属性。

• // [@属性名] 属性过滤

• // [标签名] 子元素过滤

• @Test

  //遍历所有元素节点

•  publicvoidtest2()throwsException{
              //创建一个xml解析对象
              SAXReaderreader= new SAXReader();
              //把xml文档加载到document对象中
              Documentdocument= reader.read("src/Book.xml");
              Elementroot= document.getRootElement();
              treeWalk(root);
        }
        
        privatevoidtreeWalk(Elementele){
              //输出当前节点的名字
              System.out.println(ele.getName());
              //ele.nodeCount()得到当前节点的所有子节点的数量
              for(inti= 0;i<ele.nodeCount();i++){
                    //取出下标为i的节点
                    Nodenode= ele.node(i);
                    //判断当前节点是否为标签
                    if(nodeinstanceofElement){
                          //把node强转为标签(Element)
                          treeWalk((Element)node);
                    }
              }
        }
  }

• public classTestDom4j {
        @Test
        publicvoidtest1()throwsException{
              //创建一个xml解析对象
              SAXReaderreader= new SAXReader();
              //把xml文档加载到document对象中
              Documentdocument= reader.read("src/Book.xml");
              Elementroot= document.getRootElement();
  //          Element bookNode = root.element("书");
  //          System.out.println(bookNode.getName());
              //得到当前节点所有的子节点
              Listlist= root.elements();
              //得到第二本书对象
              ElementsecondBook= (Element)list.get(1);
              //得到当前节点的文本内容
              Stringname= secondBook.element("书名").getText();
              System.out.println(name);
        }

• 导入jar包 dom4j.jar

• 创建解析器

• 解析xml 获得document对象

• SAXReader reader = new SAXReader()

• Document document = reader.read(url)

• JAXP sun公司提供的解析 支持dom和sax

• JDOM

• DOM4J dom for java民间方式，但是是事实方式，非常好，支持dom

• 解析xml

• XPATH 专门用于查询

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