I was asking the same question not long ago. Here is an easy way to return a pdf from an action method (in this case a Jasper Report):

byte[] data = JasperRunManager.runReportToPdf(compileDir
 + report.getReport() + ".jasper", params);

 FacesContext facesContext = FacesContext.getCurrentInstance();
 HttpServletResponse response = (HttpServletResponse) facesContext
 .getExternalContext().getResponse();
 response.setContentType("application/pdf");
 response.setContentLength(data.length);
 response.setHeader("Content-disposition",
 "attachment;filename=report.pdf");

 try {

 OutputStream out = response.getOutputStream();

 out.write(data);

 out.flush();
 out.close();

 facesContext.responseComplete();
 } catch (IOException ex) {
 FacesMessages.instance().add(
 "Error while downloading the file: report.pdf");
 }

Alex
How do you return reports in xls format?