Take a look at this link:

http://www.winstonprakash.com/articles/jsf/file_download_link.htm

A very simple way to do that (after you click the download button):

• Send a request to server;
• Instead processing the request and return a html to the client; you can process the request and return the FILE itself, but you will have to make some changes to you Response object:

1.    response.setContentType("application/octet-stream");  /* This will download as binary (even if you are downloading txt... you can check mimetypes for other code */
2.    response.addHeader("content-disposition", "attachment; filename=" + filename ); /* with your file name */
3.    response.setContentLength((int)file.length()); /* The size you can get from DB */
4.     ServletOutputStream out = response.getOutputStream();
5.    Inside a loop {  out.write(file content)   }

That is it!

Hope it helps

Rodolpho

Don't use a4j:commandButton. Use h:commandButton instead.

I had a very similar issue a year or so back and found a couple of issues..

Mimetype should be appropriately set for .jpg or .jpeg this should be 'image/jpeg'

I tested all these:

ID MIMETYPE

bmp image/bmp

class application/octet-streamx

css text/css

doc application/word

docm application/vnd.openxmlformats-application/vnd.ms-word.document.macroEnabled.12

docx application/vnd.openxmlformats-officedocument.wordprocessingml.document

dotm application/vnd.openxmlformats-application/vnd.ms-application/vnd.ms-word.template.macroEnabled.12

dotx application/vnd.openxmlformats-officedocument.wordprocessingml.template

exe application/octet-streamx

gif image/gif

htm text/html

html text/html

jpe image/jpeg

jpeg image/jpeg

jpg image/jpeg

mp2 video/mpeg

mp3 application/octet-streamx

mpa video/mpeg

mpe video/mpeg

mpeg video/mpeg

mpg video/mpeg

mpp application/vnd.ms-project

pdf application/pdf

pps application/vnd.ms-powerpoint

ppsx application/vnd.openxmlformats-officedocument.presentationml.slideshow

ppt application/vnd.ms-powerpoint

pptm application/vnd.ms-powerpoint.presentation.macroEnabled.12

pptx application/vnd.openxmlformats-officedocument.presentationml.presentation

rtf application/rtf

tif image/tiff

tiff image/tiff

txt text/plain

wcm application/vnd.ms-works

wdb application/vnd.ms-works

wks application/vnd.ms-works

wps application/vnd.ms-works

xla application/vnd.ms-excel

xlc application/vnd.ms-excel

xlm application/vnd.ms-excel

xls application/vnd.ms-excel

xlsx application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

xlt application/vnd.ms-excel

xlw application/vnd.ms-excel

zip application/x-zip-compressed

For some file types e.g. .pdf, you need to call context.responseComplete(); at the end of the method once all data has been transferred - but called for all types.

There are problems when it comes to handling very large files because the file has to be held in the server memory before it is send downstram; in practice, I limited the file size to 200Mb on a (virtual) server with 2Gb memory. I did sucessfull tests on 500Mb files - bit I wanted to ensure there was pleanty of headroom. 

Yes. You can use always octect-stream. It works.

Try that:

response.addHeader("content-disposition", "attachment; filename=" + "\"test.jpg\""); /* with your file name */

It should work, but if not I will take a look on my code that is already working.

The system I had starts downloading all files no matter what they are (txt; pdf;jpg;exe;bin;zip...)

--

Rodolpho

Hi Uwe.

In my JSP I have this line:

<h:commandLink type="submit" value="#{dataItem.attachName}" action="#{myBean.downloadAttachment}"/>

On MyBean:

public String downloadAttachment() {

   HttpServletResponse response =

    (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();

   try {

    Item item = itemService.getById(Item.class, new Integer(this.Id).intValue()); // Just to get the correct data from DB --- use yours here

    response.getOutputStream().write(item.getAttachData());

    response.setContentType("application");

    response.setContentLength(item.getAttachData().length);

    response.setHeader("Content-Disposition", "attachment;filename=\"" + item.getAttachName() + "\"");

    response.getOutputStream().flush();

    response.getOutputStream().close();

    FacesContext.getCurrentInstance().responseComplete();

   } catch (IOException exception) {

    System.out.println(exception.getStackTrace());

   }

  }

  return null;

}

What I saw here, is "application" only. And the Header has some caption characters, try to use as I  used on code above.

--

Rodolpho

Hello,

I try your code to download a file stored in a database but it doesn't work.

In the JSF file, I must put a <a4j:commandLink, the <h:commandLink doesn't enter in the code of the MB class.

Here is the code in my Bean class:

public String downloadAttach(BigDecimal idAttachToLoad) throws IOException

    {

        for(GsoFormAttach gfa : formsMb.getCurrentForm().getGsoFormAttachs())

        {

            if(gfa.getIdAttach().equals(idAttachToLoad))

            {

                gsoformAttach = gfa;

                HttpServletResponse response =  (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();

                try

                {

                    response.getOutputStream().write(gfa.getBlobAttach());

                    response.setContentType("application/octet-stream");

                    response.setContentLength(gfa.getBlobAttach().length);

                    response.setHeader("Content-Disposition", "attachment;filename=\"" + gfa.getFileName() + "\"");

                    response.getOutputStream().flush();

                    response.getOutputStream().close();

                }                

                catch (IOException exception)

                {

                     Logger.getLogger(Cadre5Mb.class.getName()).log(Level.SEVERE, null, exception);

                }        

            }

        }

        return null;

    }

And I have this error:

java.lang.IllegalStateException: "getOutputStream()" has already been called for this answer

I try a lot of different method to download this file but always have an error like this. I have too the error:

java.net.SocketException: Connection reset by peer: socket write error

Can someone help me please?

Do not use <a4j:commandButton , try with <h:commandButton. Ajax request not write byte content.

It doesn't work. I say in my last post: "the <h:commandLink doesn't enter in the code of the MB class."

When I click, I have the error:

ClientAbortException:  java.net.SocketException: Connection reset by peer: socket write error