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XML learning Day1: XML / jsup parser / selector /xpath selector
2022-07-27 18:34:00 【Z know and do t】
XML
1.1 XML summary
## XML：
1. Concept ：Extensible Markup Language Extensible markup language
* Scalable ： The tags are all custom . <user> <student>
* function
* Store the data
1. The configuration file
2. To transmit in a network
* xml And html The difference between
1. xml The tags are all custom ,html Tags are predefined .
2. xml The grammar is strict ,html Loose grammar
3. xml It's about storing data ,html It's showing data
* w3c: World wide web consortium
1.2 XML grammar
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. Attribute values must use quotation marks ( Single and double ) Lead up
5. Label must be closed correctly
6. xml Label names are case sensitive
* Quick start ：
<?xml version='1.0' ?>
<users>
<user id='1'>
<name>zhangsan</name>
<age>23</age>
<gender>male</gender>
<br/>
</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 , Required properties
* 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
* Value ：
* yes： Don't rely on other files
* no： Rely on other files
2. Instructions ( understand )： combination 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
* Names cannot begin with numbers or punctuation
* The name cannot be in letters xml（ perhaps XML、Xml wait ） Start
* The name cannot contain spaces
4. attribute ：
id Attribute value is unique
5. Text ：
* CDATA District ： The data in this area will be displayed as is
* Format ： <![CDATA[ data ]]>
1.3 xml constraint
* 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 read and understand constraint documents easily
* 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
* external dtd： Define the rules of constraint in the external dtd In file
* 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">
* Schema:
* introduce ：
1. Fill in xml Root element of the document
2. introduce xsi Prefix . xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3. introduce xsd File namespace . xsi:schemaLocation="http://www.itcast.cn/xml student.xsd"
4. For every one xsd Constraints declare a prefix , As identification xmlns="http://www.itcast.cn/xml"
<students xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.itcast.cn/xml"
xsi:schemaLocation="http://www.itcast.cn/xml student.xsd">
Two 、Jsoup Parser
In obtaining student.xml Of path when xml The file should be src Under the table of contents , Otherwise, a null pointer exception will occur
2.1 Jsoup Quick start
Insert a code chip here
/** * Jsoup Quick start */
public class JsoupDemo01 {
public static void main(String[] args) throws IOException {
//2.1 obtain student.xml Of path
String path = JsoupDemo01.class.getClassLoader().getResource("student.xml").getPath();
//2.2 analysis xml file , Load document into memory , obtain dom Trees --->Document
Document document = Jsoup.parse(new File(path), "utf-8");
//3. Get element object Element
Elements elements = document.getElementsByTag("name");
System.out.println(elements.size());
//3.1 Get the first one name Of element object , The index of the first object is 0
Element element = elements.get(0);
//3.2 get data
String text = element.text();
System.out.println(text);
}
}
<?xml version="1.0" encoding="UTF-8" ?>
<students>
<student number="heima_0001">
<name id="itcast">
<xing> Zhang </xing>
<ming> 3、 ... and </ming>
</name>
<age>18</age>
<sex>male</sex>
</student>
<student number="heima_0002">
<name>jack</name>
<age>18</age>
<sex>female</sex>
</student>
</students>
2.2 Jsoup_Jsoup object
* Use of objects ：
1. Jsoup： Tool class , Can be parsed html or xml file , return Document
* parse： analysis html or xml file , return Document
* parse(File in, String charsetName)： analysis xml or html Of documents .
* 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
/** * Jsoup Quick start */
public class JsoupDemo02 {
public static void main(String[] args) throws IOException {
//2.1 obtain student.xml Of path
String path = JsoupDemo02.class.getClassLoader().getResource("student.xml").getPath();
//2.2 analysis xml file , Load document into memory , obtain dom Trees --->Document
/* Document document = Jsoup.parse(new File(path), "utf-8"); System.out.println(document);// Returns the string representation of xml file */
//2. parse (String html): analysis xml or html character string
/* String str ="<?xml version=\"1.0\" encoding=\"UTF-8\" ?>\n" + "\n" + "<students>\n" + " <student number=\"heima_0001\">\n" + " <name id=\"itcast\">\n" + " <xing> Zhang </xing>\n" + " <ming> 3、 ... and </ming>\n" + " </name>\n" + " <age>18</age>\n" + " <sex>male</sex>\n" + " </student>\n" + " <student number=\"heima_0002\">\n" + " <name>jack</name>\n" + " <age>18</age>\n" + " <sex>female</sex>\n" + " </student>\n" + "\n" + "</students>"; Document document = Jsoup.parse(str); System.out.println(document);// It can also be parsed xml file */
//3.parse(URL url, int timeoutMillis)： Get the specified... Through the network path html or xml Document object for
URL url = new URL("https://www.baidu.com/");
Document document = Jsoup.parse(url, 10000);
System.out.println(document);// It can be interpreted as html file
}
}
2.3 Jsoup_document object
document Object inherited from element object
2. Document： Document object . Represents... In memory dom Trees
* obtain Element object
* getElementById(String id)： according to id Property value gets unique element object
* getElementsByTag(String tagName)： Get the collection of element objects according to the label name
* getElementsByAttribute(String key)： Get the collection of element objects according to the attribute name
* getElementsByAttributeValue(String key, String value)： Get the element object set according to the corresponding attribute name and attribute value
/** * document The function of the object */
public class JsoupDemo03 {
public static void main(String[] args) throws IOException {
//1. obtain student.xml Of path
String path = JsoupDemo03.class.getClassLoader().getResource("student.xml").getPath();
//2. obtain document object
Document document = Jsoup.parse(new File(path), "utf-8");
//3. Get element object .
//3.1 Get all student object
Elements elements = document.getElementsByTag("student");
System.out.println(elements);
System.out.println("-------------");
//3.2 Get the property named id Element objects
Elements elements1 = document.getElementsByAttribute("id");
System.out.println(elements1);
//3.2 obtain number The property value is heima_0001 The element object of
Elements elements2 = document.getElementsByAttributeValue("number", "heimai_0001");
System.out.println(elements2);
//3.3 obtain id Element object of attribute value
Element itcast = document.getElementById("itcast");
System.out.println(itcast);
}
}
2.4 Jsoup_Element object
3. Elements： Elements Element A collection of objects . Can be regarded as ArrayList<Element> To use
4. Element： Element object
1. Get child element object
* getElementById(String id)： according to id Property value gets unique element object
* getElementsByTag(String tagName)： Get the collection of element objects according to the label name
* getElementsByAttribute(String key)： Get the collection of element objects according to the attribute name
* getElementsByAttributeValue(String key, String value)： Get the element object set according to the corresponding attribute name and attribute value
2. Get attribute value
* String attr(String key)： Get the property value according to the property name
3. Get text content
* String text(): Get text content
* String html(): Get all the contents of the label body ( Include the string content of the word tag )
5. Node： Node object
* yes Document and Element Parent class of
2.4 Jsoup_ according to Selector query
* 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 , It's a way to determine XML（ A subset of Standard General Markup Languages ） 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
/** * Selector query */
public class JsoupDemo05 {
public static void main(String[] args) throws IOException {
//1. obtain student.xml Of path
String path = JsoupDemo05.class.getClassLoader().getResource("student.xml").getPath();
//2. obtain document object
Document document = Jsoup.parse(new File(path), "utf-8");
//3. Inquire about name label
/* div{ } */
Elements elements = document.select("name");
System.out.println(elements);
System.out.println("----------");
//4. Inquire about id The value is itcast The elements of id Selectors How to write it ： #id
Elements elements1 = document.select("#itcast");
System.out.println(elements1);
System.out.println("-----------");
//5. obtain student Label and number The property value is heima_0001 Of age Child tags
//5.1 obtain student Label and number The property value is heima_0001
Elements elements2 = document.select("student[number=\"heima_0001\"]");
System.out.println(elements2);
System.out.println("-----");
//5.2 obtain student Label and number The property value is heima_0001 Of age Child tags
Elements elements3 = document.select("student[number=\"heima_0001\"] > age");
System.out.println(elements3);
}
}
2.4 Jsoup_ according to Xpath Inquire about
XPath：XPath That is to say XML Path to the language , It's a way to determine XML（ A subset of Standard General Markup Languages ） 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
/** * Xpath Inquire about */
public class JsoupDemo06 {
public static void main(String[] args) throws IOException, XpathSyntaxErrorException {
//1. obtain student.xml Of path
String path = JsoupDemo06.class.getClassLoader().getResource("student.xml").getPath();
//2. obtain document object
Document document = Jsoup.parse(new File(path), "utf-8");
//3. according to document object , establish JXDocument object
JXDocument jxDocument = new JXDocument(document);
//4. combination xpath Syntax query
//4.1 Query all student object
List<JXNode> jxNodes = jxDocument.selN("//student");
for (JXNode jxNode : jxNodes) {
System.out.println(jxNode);
}
System.out.println("------------");
//4.2 Inquire about student Label under name label
List<JXNode> jxNodes1 = jxDocument.selN("//student/name");
for (JXNode jxNode : jxNodes1) {
System.out.println(jxNode);
}
System.out.println("--------------");
//4.3 Inquire about student There is... Under the label id Attribute name label
List<JXNode> jxNodes2 = jxDocument.selN("//student/name[@id]");
for (JXNode jxNode : jxNodes2) {
System.out.println(jxNode);
}
System.out.println("---------------");
//4.4 Inquire about student There is... Under the label id Attribute name label , also id The property value of is itcast
List<JXNode> jxNodes3 = jxDocument.selN("//student/name[@id='itcast']");
for (JXNode jxNode : jxNodes3) {
System.out.println(jxNode);
}
}
}
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