How to pass a Console output to show as a pop up box in browser

I have a java code which outputs an Alert if it meet some condition. I am setting that value as below.

message = "Alert, Net Usage greater than or equal to threshold";
System.out.println(message);
request.setAttribute("message",message);
 RequestDispatcher dispatcher = request.getRequestDispatcher("jsppage.jsp");
 dispatcher.forward(request, response);

I want to display the "message" in a pop up in the browser. Please help.