Download Excel

The way I solved it was the following:

False the ajax property of the xhtml:

<h:form>
    <p:commandButton action="#{controller.descargar}"
        value="descargar" ajax ="false"/>
</h:form>

Bean:

@Named(value = "controller")
@SessionScoped 
public class ClientsCtrl {
    public void descargar(){
    //Obtenemos el contexto de jsf
    FacesContext fc = FacesContext.getCurrentInstance();
    ExternalContext ec = fc.getExternalContext();
    //Le asignamos un nombre
    String name = "Mi excel.xls");
    ec.responseReset();
    //Esto es importante y tiene que ver con el tipo de archivo, esté 
        //caso es para un excel
    ec.setResponseHeader("Content-Type", application/vnd.ms-excel));
    ec.setResponseHeader("Content-Disposition", "attachment; filename=\"" + name + "\"");
    //Trataremos de obtener un outputStream
    try (OutputStream output = ec.getResponseOutputStream()) {
    //Invocamos el objeto que devuelve el excel y le pasamos el outputStream
        GeneraExcel gExcel = new GeneraExcel();
    gExcel.crearExcel(output;

        //Con esto obtenemos el tamaño del archivo
        try (CountingOutputStream co = new CountingOutputStream(output)) {
            ec.setResponseContentLength((int) co.getByteCount());
            co.close();
        } catch (IOException ex) {
            System.out.println("Error al obtener el tamaño del stream " + ex.getMessage());
        }
    } catch (Exception e) {
        System.out.println("Error al intentar crear el excel " + e.getMessage());
    }

    fc.responseComplete();
    }
}

GeneratesExcel:

public class GeneraExcel {
//Cambie mucho la implementación de esta parte, pero el resultado es el mismo.
//Entre los cambios importantes es que ahora solicito un OutputStream

    public void crearExcel(OutputStream outputStream) {
          try {
        Workbook wb = new HSSFWorkbook();
        Sheet sheet = wb.createSheet("MySheet");
        CreationHelper createHelper = wb.getCreationHelper();

        // Create a row and put some cells in it. Rows are 0 based.
        Row row = sheet.createRow((short) 0);
        Cell cell = row.createCell(0);
        cell.setCellValue(1);
        row.createCell(1).setCellValue(1.2);
        row.createCell(2).setCellValue(createHelper.createRichTextString("This is a string"));
        row.createCell(3).setCellValue(true);
        row.createCell(5).setCellValue("soy el 5");



        row = sheet.createRow(3);
        cell.setCellValue("hola");   
     row.createCell(6).setCellValue("soy el 6");

     //Escribimos sobre el outputStrream y luego le hacemos flush y lo cerramos para sincronizarlo
        wb.write(outputStream);
        outputStream.flush();
        outputStream.close();

    } catch (IOException ex) {
        System.out.println(ex);
    }
    }

}

It would probably serve you something like this, intercepting it with an ajax command

<p:commandButton value="Download" ajax="false" onclick="PrimeFaces.monitorDownload(start, stop);" icon="ui-icon-arrowthick-1-s">
        <p:fileDownload value="#{fileDownloadView.file}" />
</p:commandButton>

In the controller part:

@ManagedBean
public class FileDownloadView {

    private StreamedContent file;

    public FileDownloadView() {        
        InputStream stream = FacesContext.getCurrentInstance().getExternalContext().getResourceAsStream("/resources/demo/images/optimus.jpg");
        file = new DefaultStreamedContent(stream, "image/jpg", "downloaded_optimus.jpg");
    }

    public StreamedContent getFile() {
        return file;
    }
}

You have the complete example in the primefaces documentation

link

Sincerely,