Renderizar PDF + jasper + jsf

public static void abrirRelatorio(byte[] bytes, String fileName) throws Exception {
		if (bytes == null)
			throw new Exception("Array de bytes nulo.");

		if (fileName == null)
			throw new Exception("Nome do arquivo é nulo.");

		FacesContext facesContext = FacesContext.getCurrentInstance();
		HttpServletResponse response = (HttpServletResponse) facesContext
				.getExternalContext().getResponse();
		response.setHeader("Content-Disposition", "attachment; filename=\""
				+ fileName + "\";");
		response.setContentLength(bytes.length);
		ServletOutputStream ouputStream = response.getOutputStream();
		ouputStream.write(bytes, 0, bytes.length);
		facesContext.responseComplete();
	}

         public void gerarRelatorio() throws Exception {
		FacesContext facesContext = FacesContext.getCurrentInstance();
		ServletContext servletContext = (ServletContext) facesContext
				.getExternalContext().getContext();
		String pathRel = servletContext
				.getRealPath("/relatorio/rota_parada.jasper");
		// parametros
		Map<String, Object> parameters = new HashMap<String, Object>();
		parameters.put("filtro", getFiltro());
		parameters.put("imagem", servletContext
				.getRealPath("/img/logogafor.gif"));
		parameters.put("powered", servletContext
				.getRealPath("/img/powered.gif"));

		// recebe por parametro uma lista da propia classe jah populada
		JRDataSource coll = new JRResultSetDataSource(rotaService
				.getRotasRelatorioResult(rota, placaCarreta, produtoId,
						placaVeiculo, cidade, estado, motorista, dataInicial,
						dataFinal, cliente, statusID));

		try {
			JasperPrint print = JasperFillManager.fillReport(pathRel,
					parameters, coll);
			byte[] bytes = JasperExportManager.exportReportToPdf(print);
			Util.abrirRelatorio(bytes, "ListaViagens.pdf");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}