XML Learning Summary-xpath technology-(ii)

XPath technology

When using a dom4j query to compare deep hierarchies of nodes (labels, text, attributes), it is cumbersome to have the XPath technology appear

XPath function: Used to quickly get the desired node object

How to use XPath technology in DOM4J

1) Import the XPath support jar package. Jaxen-1.1-beta-6.jar

2) using the XPath method

List <Node> selectnodes ("XPath expression"); Querying multiple Node objects

Node selectSingleNode ("XPath expression"); Querying a Node object

XPath syntax

/absolute path represents the beginning of the root position of the XML or child element (a hierarchy)

A relative path represents a selection element that is not divided into any hierarchy.

* Wildcard means matching all elements

[] condition indicates which element is selected under what conditions

The @ property represents the Select Attribute node

and relationships (equivalent to &&) of conditions

Text () literal indicates selection of text content

Delete the specified label

Package Gz.itcast.b_xpath;import Java.io.file;import Java.io.fileoutputstream;import org.dom4j.document;import Org.dom4j.element;import Org.dom4j.io.outputformat;import Org.dom4j.io.saxreader;import org.dom4j.io.XMLWriter;/* * * First XPath program * @author APPle * */public class Demo1 {public static void main (string[] args) throws exception{/** * Requirements: Delete Except the student tag with ID value 2 */document doc = new Saxreader (). Read (New File ("E:/student.xml"));//1. Student with ID 2 tag//use XPath technology element Stuelem = (Element) doc.selectsinglenode ("//student[@id = ' 2 ')",//2. Delete label Stuelem.detach ();//3. Write out the xml file FileOutputStream out = new FileOutputStream ("E:/student.xml"); OutputFormat format = Outputformat.createprettyprint (); Format.setencoding ("Utf-8"); XMLWriter writer = new XMLWriter (Out,format); Writer.write (doc); Writer.close ();}}

Package Gz.itcast.b_xpath;import Java.io.file;import Java.util.list;import org.dom4j.document;import Org.dom4j.Node  Import org.dom4j.io.saxreader;/** * Learn XPath expression syntax * @author APPle * */public class Demo2 {public static void main (string[] args) throws Exception {Document doc = new Saxreader (). Read (New File ("./src/contact.xml"));  String XPath = "";/** * 1. The/absolute path represents the beginning of the root position of the XML or child element (a hierarchy) */xpath = "/contactlist"; xpath = "/contactlist/contact";/** * 2. A relative path represents a selection element that is not divided into any hierarchy. */xpath = "//contact/name"; xpath = "//name";/** * 3. * Wildcard means match all elements */xpath = "/contactlist/*"; All child tags under the root tag contactlist xpath = "/contactlist//*";//All labels under the root tag contactlist (no hierarchy)/** * 4. [] Conditions indicate what conditions are selected for the element *///with the id attribute of the contact label XPath = "//contact[@id]";//the second contact tag XPath = "//contact[2]";//Select the most After a contact tag XPath = "//contact[last ()]";/** * 5. The @ attribute indicates the Select attribute node */xpath = "//@id"; Select the id attribute node object that returns the attribute object XPath = "//contact[not (@id)]";//select the contact label node that does not contain the id attribute XPath = "//contact[@id = ' 002 ']";//select the contact label with the value 002 for the id attribute xpath = "//contact[@id = ' 001 ' and @name = ' Eric ']";//select the id attribute value 001,  and the Name property is Eric's contact label/** *6. Text () to select text content *///Select the text content under the name label, return text Object XPath = "//name/text ()"; XPath = "//contact/name[text () = ' Zhang San ']";// Select the name Zhang San name tag list<node> list = Doc.selectnodes (XPath); for (node node:list) {System.out.println (node);}}}

　　

Read XML file impersonate user login

Package Gz.itcast.b_xpath;import Java.io.bufferedreader;import Java.io.file;import java.io.InputStreamReader; Import Org.dom4j.document;import org.dom4j.element;import org.dom4j.io.saxreader;/** * XPath case: Impersonate user Login Effect * @author APPle * */public class Demo3 {public static void main (string[] args) throws exception{//1. Gets the user name and password entered by the user bufferedreader br = New BufferedReader (New InputStreamReader (system.in)); System.out.println ("Please enter user name:"); String name = Br.readline (); System.out.println ("Please enter password:"); String password = br.readline ();//2. To the database, query whether there is a corresponding user//corresponding User:  found in the User.xml file a   //name attribute value of ' User input ', and the password attribute value is ' user input ' of the username doc = new Saxreader (). Read (New File ("./src/user.xml")); Element Userelem = (Element) Doc.selectsinglenode ("//user[@name = '" +name + "and @password = '" +password+ "']"); if ( Userelem!=null) {//Login succeeded System.out.println ("login Successful");} else{//Login failed System.out.println ("Login Failed");}}}

Reading HTML Document contents

 
 
Package Gz.itcast.b_xpath;import Java.io.file;import Java.util.iterator;import java.util.list;import Org.dom4j.document;import Org.dom4j.element;import org.dom4j.io.saxreader;/** * Use XPath technology to read a canonical HTML document * @author APPle * */public class Demo4 {public static void main (string[] args) throws exception{document doc = new Saxreader (). Read ( New File ("./src/personlist.html"));//system.out.println (doc);//Read title tag Element Titleelem = (Element) Doc.selectsinglenode ("//title"); String title = Titleelem.gettext ();  System.out.println (title);/** * Exercise: Read all information about a contact * output in the following format: * No.: 001 name: Zhang San Sex: Male Age: 18 Address: xxxx Tel: xxxx * No: 002 Name: John Doe Gender: Female Age: 20 Address: xxxx Tel: xxxx * ... *///1. Read all tbody in the TR label list<element> list = (list<element>) doc.sele Ctnodes ("//tbody/tr");//2. Traverse for (element Elem:list) {//number//string id = (element) elem.elements (). Get (0)). GetText (); String id = Elem.selectsinglenode ("td[1]"). GetText ();//Name String name = (Element) elem.elements (). Get (1)). GetText (); /gender String gender =(Element) elem.elements (). Get (2)). GetText ();//Age string ages = (Element) elem.elements (). Get (3)). GetText ();/ Address string = (Element) elem.elements (). Get (4)). GetText ();//Telephone string phone = (element) elem.elements (). Get (5)). GetText (); System.out.println ("Number:" +id+ "\ t name:" +name+ "\ T Gender:" +gender+ "\ T Age:" +age+ "\ T address:" +address+ "\ t Tel:" +phone);}}}
　
XML Learning Summary-xpath technology-(ii)