Ajax is used to determine if a user is enrolled in an instance tutorial

This article is mainly for everyone in detail the Ajax used to determine whether the user registration, has a certain reference value, interested in small partners can refer to, hope to help everyone.

On many registered pages, we may encounter the following situations, when we register the user name may prompt that the user name is registered, the implementation is the application of Ajax technology.

First write a landing page

Import Java.io.ioexception;import java.io.printwriter;import java.sql.connection;import Java.sql.DriverManager; Import Java.sql.preparedstatement;import Java.sql.resultset;import Java.sql.sqlexception;import Javax.servlet.servletexception;import Javax.servlet.http.httpservlet;import Javax.servlet.http.httpservletrequest;import Javax.servlet.http.httpservletresponse;public class CheckServlet Extends httpservlet{public static final string dbdriver = "Oracle.jdbc.OracleDriver";p ublic static final String dburl = "J Dbc:oracle:thin:@59.173.240.149:1521:heer ";p ublic static final String DBUSER =" Hnsyu_dev ";p ublic static final string Dbpass = "Hnsyuok";p ublic void doget (httpservletrequest request,httpservletresponse response) throws Servletexception, Ioexception{this.dopost (request, response);} public void DoPost (HttpServletRequest request,httpservletresponse response) throws servletexception,ioexception{ Request.setcharacterencoding ("GBK"); Response.setcontenttype ("text/html"); Connection Connection= NULL; PreparedStatement preparedstatement = null; ResultSet ResultSet = null; PrintWriter out = Response.getwriter (); String UserID = request.getparameter ("userid"); try {class.forname (dbdriver); connection = Drivermanager.getconnection (Dburl, DBUSER, Dbpass); String sql = "SELECT COUNT (userid) from Userdemo where userid=?"; PreparedStatement = connection.preparestatement (sql);p reparedstatement.setstring (1,userid); ResultSet = Preparedstatement.executequery (), if (Resultset.next ()) {if (Resultset.getint (1) >0) {Out.print ("false"); System.out.println ("true");} else {Out.print ("false");}} Out.close ();} catch (Exception e) {e.printstacktrace ();} Finally{try {connection.close ();} catch (Exception e) {e.printstacktrace ();}}}}
It also needs to be configured in Web. xml



<?xml version= "1.0" encoding= "UTF-8"? ><web-app version= "3.0" xmlns= "Http://java.sun.com/xml/ns/javaee" Xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation= "Http://java.sun.com/xml/ns/javaee http ://java.sun.com/xml/ns/javaee/web-app_3_0.xsd "> <display-name></display-name>  < welcome-file-list>  <welcome-file>index.jsp</welcome-file> </welcome-file-list>  <servlet> <servlet-name>CheckServlet</servlet-name> <servlet-class>checkservlet</ servlet-class> </servlet> <servlet-mapping> <servlet-name>CheckServlet</servlet-name> <url-pattern>/CheckServlet</url-pattern> </servlet-mapping> </web-app>
Have you learned it? Feel good hurry up and collect it.