XML file usage and parsing

One 、 summary

Xml and html It's all a markup language , however xml Is an extensible markup language , It is extensible , about html All marks, such as ,<a> Represents a connection . All have a certain meaning , You can't define some labels by yourself , however xml You can customize some labels . For data transfer

<?xml version="1.0" encoding="UTF-8"?>
<!-- The above sentence is xml documentation   Must be on the first line -->
<!-- every last xml There is a root tag that contains child tags   And it is divided into case -->
<goodlist>
    <!-- Each sub tag has its own attributes   such as id attribute -->
    <good id="111">
        <name>apple</name>
        <place>beijing</place>
    </good>
    <good>
        <name>banana</name>
        <place>shanghei</place>
    </good>
</goodlist>

Two 、 Constraint file

Usually written xml file , There are no fixed rules , Tag name Property name Attribute values can be defined at will , But if you want others to use yourself xml The use of documents , Relevant labels cannot be defined randomly , It's here xml Add constraint file to the file , There are two common constraint files DTD（ The file name suffix is dtd） and schema（ The file name suffix is xsd） Two kinds of , By comparison ,schema Constraint files are more advanced and comprehensive .DTD Constraints and schema constraint （ It's the same thing It's just that it's powerful and different ）

Location

Inside dtd

external dtd

3、 ... and 、 analysis

summary

1. JAXP：sun Company supplied parsers , Support dom and sax Two thoughts

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：Android The built-in parser of the operating system ,sax The way of .

DOM4J analysis

The way is dom The way , hold xml The file is loaded into memory to form a dom Trees

And get a document object . have access to dom4j Conduct dom Analysis of the way

take Dom4j Of jar Put the package in the project root directory and create a folder as lib（javase engineering ）;web The project is directly put into WEB-INF Medium lib file

You can also use dom4j Generate xml file

perhaps

result

 

jsoup analysis

summary

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 .

* step ：

      1. Import jar package

      2. obtain Document object

      3. Get the corresponding label Element object

      4. get data

Case code

		// obtain student.xml Of path
        String path = JsoupDemo1.class.getClassLoader().getResource("student.xml").getPath();
        // analysis xml file , Load document into memory , obtain dom Trees --->Document
        Document document = Jsoup.parse(new File(path), "utf-8");
        // Get element object  Element
        Elements elements = document.getElementsByTag("name");

        System.out.println(elements.size());
        // Get the first one name Of Element object 
        Element element = elements.get(0);
        // get data 
        String name = element.text();
        System.out.println(name);

Using document

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

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

3. Elements： Elements Element A collection of objects . Can be regarded as ArrayList<Element> To use

4. Element： Element object

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

Get attribute value
* String attr(String key)： Get the property value according to the property name

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

*6. Quick query

selector: Selectors
* Method used ：Elements   select(String cssQuery)

* grammar ： Reference resources Selector Syntax defined in class

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
* Code ：

//1. obtain student.xml Of path
String path = JsoupDemo6.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);

combination xpath Syntax query

// Query all student label 
List<JXNode> jxNodes = jxDocument.selN("//student");
    for (JXNode jxNode : jxNodes) {
    System.out.println(jxNode);
    }
    System.out.println("--------------------");

// Query all student Label under name label 
    List<JXNode> jxNodes2 = jxDocument.selN("//student/name");
        for (JXNode jxNode : jxNodes2) {
        System.out.println(jxNode);
        }
        System.out.println("--------------------");

// Inquire about student There is... Under the label id Attribute name label 
        List<JXNode> jxNodes3 = jxDocument.selN("//student/name[@id]");
            for (JXNode jxNode : jxNodes3) {
            System.out.println(jxNode);
            }
            System.out.println("--------------------");

// Inquire about student There is... Under the label id Attribute name label   also id The property value is itcast
            List<JXNode> jxNodes4 = jxDocument.selN("//student/name[@id='itcast']");
                for (JXNode jxNode : jxNodes4) {
                System.out.println(jxNode);
                }