package javax.servlet does not exist in netbeans

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Java

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netbeans

hi i am developing an application in netbeans.
in that following error occured
"package javax.servlet does not exist"

this is the code

package child;

import java.sql.*;
import java.io.*;
import javax.servlet.ServletException;//error package javax.servlet does not exist 
import javax.servlet.http.HttpServlet;//error package javax.servlet does not exist 
import javax.servlet.http.HttpServletRequest;//error package javax.servlet does not exist 
import javax.servlet.http.HttpServletResponse;//error package javax.servlet does not exist 
import javax.servlet.http.HttpSession;//error package javax.servlet does not exist 


public class addnewphonenumber extends HttpServlet {//error "cannot find symbol"
  


String na1;
int c;
    
     protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
       
       response.setContentType("text/html");
       PrintWriter pout =response.getWriter();
       if(request.getParameter("oks") != null)
      {
        try{
            String flag1="no";
              Dbload db=new Dbload();
       Connection con=db.getConnection();
       
       ResultSet rs;
            PreparedStatement ps;
            String mob= request.getParameter("mobile");
            na1=request.getParameter("str");
            
            ps= (PreparedStatement) con.prepareStatement("select * from login where username=?");
            ps.setString(1,na1);
            rs=ps.executeQuery();
            if(rs.next())
            c=rs.getInt(1);
            ps.close();
            ps=con.prepareStatement("insert into mobnumbers(id,mob,flag) values(?,?,?);");
            ps.setInt(1,c);
            ps.setString(2,mob);
            ps.setString(3, flag1);
            ps.executeUpdate();
           ps.close();
           con.close();
           response.sendRedirect("blank.jsp");
        }
        catch(SQLException e){
               response.sendRedirect("addphone.jsp");
        }
     }
        
    }
        
    }

Please help me to solve this error.
Thank you....