ActionConfig ac = new ActionCofig("/geraRelatorio", ActionRelatorio.class);
ac.addConsequence(ActionRelatorio.SUCCESS, new StreamConsequence("application/pdf"));
//...

private void processaRelNc(HttpServletRequest req, HttpServletResponse resp) throws IOException
	{
		String rnc = req.getParameter("numRnc");
		String empresa= req.getParameter("empresa");
		ErrosAplicacao erro= new ErrosAplicacao();
		erro.setLogger(Logger.getLogger(ServletGeraRelatorio.class));
		if (rnc==null)
		{
			resp.sendRedirect("/relNaoConformidade.jsp");
			erro.setErro("Valor rnc: "+ rnc, new Exception());			
		}
		String CAMINHO_ARQUIVO = "C://Relatorios//";
		resp.setHeader("Content-disposition","attachment;filename=relRnc.pdf");
		resp.setContentType("application/pdf");
		
		ServletOutputStream out = resp.getOutputStream();	
			
		HashMap mp = new HashMap();
		mp.put("rnc",rnc);
		JRResultSetDataSource jrRS = null; 
		AdminNc adm;
		try {					
			adm = new AdminNc();
			jrRS = new JRResultSetDataSource( adm.getDadosRnc(rnc,empresa));
		}catch (Exception e)
		{
			e.printStackTrace();
			erro.setLogger(Logger.getLogger(ServletGeraRelatorio.class));
			erro.setErro("Erro ao recuperar dados: ", e);
		}
		try{						
			byte[] bytes = JasperRunManager.runReportToPdf(CAMINHO_ARQUIVO + "relRnc.jasper", mp, jrRS);
			resp.setContentLength(bytes.length);
			ServletOutputStream ouputStream = resp.getOutputStream();
			ouputStream.write(bytes, 0, bytes.length);
			ouputStream.flush();
			ouputStream.close();
			
		} catch (Exception e) {
			e.printStackTrace();
			erro.setLogger(Logger.getLogger(ServletGeraRelatorio.class));
			erro.setErro("Erro ao gerar relatorio RNC: ", e);
		}
	}