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Take you to a deeper understanding of XML

Y2JOriginal: 2017-04-26 10:12:081565browse

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

Escape characters>
The data inside CDATA will be displayed as it is

#19791207a4e0a22c816ac020ecd8cae0

Processing instructions: Basically no need now

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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" ?>

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<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 filea5dfb9c8da626e491c0e8e2104dc79df
Network dtd filea32d1fb3a7dc5a5b87f11aea37d08186

<!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

If xml is used as a configuration file: read

XML parsing ideas:

Advantages: Does not occupy memory, fast

Commonly used parsers for xml

define a rule

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()
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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