RequestDispatcher rd = request.getRequestDispatcher("my.jsp?search_for");

request.setAttribute("paramName", search_for);
RequestDispatcher rd = request.getRequestDispatcher("my.jsp");
rd.forward(request, response);

RequestDispatcher rd = request.getRequestDispatcher("my.jsp?paramName="+search_for);
rd.forward(request, response);

request.setAttribute("search_for", "some value");
RequestDispatcher rd = request.getRequestDispatcher("my.jsp");
rd.forward(request, response);