Problema com setHeader

public ActionForward relatorio(ActionMapping mapping, ActionForm aform, HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		ComparacaoCustoMedioForm form = (ComparacaoCustoMedioForm) aform;
		ComparacaoCustoMedioGrid grid = new ComparacaoCustoMedioGrid();


		try {	
	            /** seta o cabeçalho para o pdf **/
				setDefaultHeader(response);
				response.setContentType("application/pdf");
				response.setHeader("Content-Disposition",
				"attachment; filename=ArquivoComparativoCustoMedio.pdf");
	            
	            //Gera conteudo em PDF
				byte[] output = rel.gerarPDF2Stream();
				response.getOutputStream().write(output);
	         
			}
			
		} catch (ExcecaoDeApresentacao ex) {
			pararPropagacao(request, ex);
			prepararPesquisa(mapping, form, request, response, null);
			mapping.findForward("pesquisar");
		}
		
		prepararPesquisa(mapping, form, request, response, null);
		return mapping.findForward("gerar");
	}