Execute backing bean action on load?

Question

I would like to build a results page for a report export page. This results page must display the status of the export and offer the download of this export.

The exp

Answer 1

You can also solve this in JSF 2.0 using component system events, specifically the PreRenderViewEvent.

Just create a download view (/download.xhtml) that fires a download listener before render.

Then, in your report bean (defined using JSR-299), you push the file and mark the response as complete.

public @Named @RequestScoped class ReportBean {

   public void download() throws Exception {
      FacesContext ctx = FacesContext.getCurrentInstance();
      pushFile(
           ctx.getExternalContext(),
           "/path/to/a/pdf/file.pdf",
           "file.pdf"
      ); 
      ctx.responseComplete();
   }

   private void pushFile(ExternalContext extCtx,
         String fileName, String displayName) throws IOException {
      File f = new File(fileName);
      int length = 0; 
      OutputStream os = extCtx.getResponseOutputStream();
      String mimetype = extCtx.getMimeType(fileName);

      extCtx.setResponseContentType(
         (mimetype != null) ? mimetype : "application/octet-stream");
      extCtx.setResponseContentLength((int) f.length());
      extCtx.setResponseHeader("Content-Disposition",
         "attachment; filename=\"" + displayName + "\"");

      // Stream to the requester.
      byte[] bbuf = new byte[1024];
      DataInputStream in = new DataInputStream(new FileInputStream(f));

      while ((in != null) && ((length = in.read(bbuf)) != -1)) {
         os.write(bbuf, 0, length);
      }  

      in.close();
   }
}

That's all there is to it!

You can either link to the download page (/download.jsf), or use a HTML meta tag to redirect to it on a splash page.