<script>
        function getCustomerDetailsAjax(str) {
            str = $('#customerId').val();

            if (document.getElementById('customerId').value <= 0) {
                document.getElementById('firstName').value = " ";
                document.getElementById('telephone').value = " ";
                document.getElementById('vehicleMake').value = " ";
                document.getElementById('vehicleModel').value = " ";
                document.getElementById('vehicleColor').value = " ";
            } else {
                $.ajax({
                    url: "GetCustomerDetails",
                    type: 'POST',
                    data: {customerId: str},
                    success: function (data) {
                        alert(data); //I want to get 2 servlet values and alert them here. How can I do that?
                    }
                });
            }
        }
    </script>

public class GetCustomerDetails extends HttpServlet {

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    PrintWriter out=response.getWriter();
    int customerId = Integer.valueOf(request.getParameter("customerId"));
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost/Vehicle", "root", "");
        PreparedStatement ps = con.prepareStatement("SELECT fistname,telephone FROM customers WHERE customerid=?");
        ps.setInt(1, customerId);
        ResultSet result=ps.executeQuery();
        if(result.next()){
            out.print(result.getString("firstname")); //I want to send this value
            out.print(result.getString("telephone")); //and this value

        }

    } catch (ClassNotFoundException ex) {
        Logger.getLogger(GetCustomerDetails.class.getName()).log(Level.SEVERE, null, ex);
    } catch (SQLException ex) {
        Logger.getLogger(GetCustomerDetails.class.getName()).log(Level.SEVERE, null, ex);
    }

}

@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>

success: function (data) {
            alert(data); //I want to get 2 servlet values and alert them here. How can I do that?
       }