User name validation using ajax in servlet

step 1: create table

create table ajax(name varchar(25),pwd varchar(25));

Step 2: insert some values

insert into ajax values('abc','abc');

table is created as follow

Step 3: create user form with ajax validation code

<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function prudhvi()
{

var xmlhttp;
if (window.XMLHttpRequest)
{
xmlhttp=new XMLHttpRequest();
}
else
{

xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
// alert("nnnnnn2");
document.getElementById("id").innerHTML=xmlhttp.responseText;
}
}
//alert("nnnnnn3");
var a=document.getElementById("name").value;
// alert(a);
xmlhttp.open("GET","s?q="+a,true);
xmlhttp.send();
}
</script>
</head>

<body>
<div id="id"></div>

UserName: <input type="text" name="name" id="name" onkeyup="prudhvi()">

</body>
</html>

Step 4: write servlet program

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 javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EmployeeServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");

// System.out.println("hello from servlet");
PrintWriter out = response.getWriter();
String ss=request.getParameter("q");
// System.out.println(ss+"*****************");
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/xxx", "root", "root");
PreparedStatement ps=con.prepareStatement("select * from ajax where name=?");
ps.setString(1,ss);
ResultSet rs=ps.executeQuery();
if(rs.next()){
out.println("name is already exist");
}
else
out.println("name doesnot already exist");

}catch(Exception e){
e.printStackTrace();
}
}

}

Step 5: generate web.xml file as below by using form and servlet

<?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">

<servlet-name>EmployeeServlet</servlet-name>

<servlet-class>EmployeeServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>EmployeeServlet</servlet-name>

<url-pattern>/s</url-pattern>

</servlet-mapping>

<session-config>

<session-timeout>

</session-timeout>

</session-config>

</web-app>