Solve my code

import javax.servlet.*;

import javax.servlet.http.*;

import java.sql.*;

import java.io.*;

public class ChangeDetails extends HttpServlet{

public void doPost(HttpServletRequest

request,HttpServletResponse response)throws ServletException, IOException{

response.setContentType("text/html");

response.setHeader("cache-control","no-cache");

PrintWriter out=response.getWriter();

String UserName=request.getParameter("uname");

String OldPassword=request.getParameter("opassword");

String NewPassword=request.getParameter("npassword");

Connection con=null;

String uid="";

String pass="";

try{

Class.forName("oracle.jdbc.driver.OracleDriver");

con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","bms","abc");

Statement stmt=con.createStatement();

ResultSet rs=stmt.executeQuery("select uname,password from userdetails");

while(rs.next()){

uid=rs.getString("uname");

pass=rs.getString("password"); }

if(pass.equals(OldPassword)){

Statement st1=con.createStatement();

st1.executeUpdate("update userdetails set

password='"+NewPassword+"' where uname='"+UserName+"'");

out.println("Password changed successfully");

con.close(); }

else{

out.println("Invalid Old Password");

}

}catch(Exception e){ }

}

}

what is the mistake in this code! This is working only one record doesn't work multiple records