refresh option is servlet

Question

Hi, I am having the below code in a servlet. I wnat these lines of code to refresh every 30 seconds automatically. I dont want the other code that is present in servlet to refresh out.println(""); out.println(""); out.println("");

                  out.println("<frame src= \"unlock.html\">");

        out.println("</frameset>");

        out.println("</HTML>");

Thanks in advance