I can do better then that. Here is a zip containing a demo program w/ an example of the code itself.

http://notpublic.zy.ca/demo.zip

In addition to Ajax4JSF (1.1.0), it needs Jakarta POI (for the excel bit). I'm currently using 3.0.0 alpha3, but it was occurring under 2.5.1 final as well and this example isn't embedding images so there is no point going to 3.0.0 alpha3.

Downloadable here:
http://www.apache.org/dyn/closer.cgi/jakarta/poi/

I'm pretty sure what is causing the problem is this bit in the action:

FacesContext fc = FacesContext.getCurrentInstance ();
HttpServletResponse response = (HttpServletResponse)fc.getExternalContext ().getResponse ();
response.setHeader ("Content-disposition", "attachment; filename=test.xls");
response.setContentType ("application/vnd.ms-excel");
ServletOutputStream out = response.getOutputStream ();

...

wb.write (out);
out.close ();
fc.responseComplete ();

It is changing the JSF state ... and thus invalidating the A4J stuff ... going to the page again fixed the problem ... but there has to be a way to do this without messing everything up.

Nope, not yet. There was another thread where a solution was suggested, but it didn't work.

Works!

Don't use actions, use a PhaseListener. Intercept a request to the page, mark it somehow (in my test, i added a parameter ?export and looked for that ... I used a normal link). And then use what you had in the action to generate the file. Everything is still there in the viewstate and your a4j actions still work fine.

Sure:

public class ExcelExportPhaseListener
 implements PhaseListener
{
 public void afterPhase (PhaseEvent phaseEvent)
 {
 FacesContext facesContext = phaseEvent.getFacesContext ();
 Map map = facesContext.getExternalContext ().getRequestParameterMap ();

 if(map.containsKey ("exportToExcel"))
 {
 try
 {
 // Create Workbook
 HSSFWorkbook wb = new HSSFWorkbook ();
 HSSFSheet sheet = wb.createSheet ("example");

 // YOUR EXCEL CODE HERE

 // IIRC, this could be a portal reponse as well, but I'm not in a portal environment so all is good.
 HttpServletResponse contextResponse = (HttpServletResponse)facesContext.getExternalContext().getResponse();

 contextResponse.setHeader ("Content-disposition", "attachment; filename=test.xls");
 contextResponse.setContentType ("application/vnd.ms-excel");

 wb.write (contextResponse.getOutputStream());
 facesContext.getApplication().getStateManager().saveSerializedView(facesContext);
 facesContext.responseComplete();
 }
 catch (Exception e)
 {
 throw new RuntimeException ( e );
 }
 }
 }

 public void beforePhase (PhaseEvent phaseEvent)
 {
 //do nothing
 }

 public PhaseId getPhaseId ()
 {
 return PhaseId.RESTORE_VIEW;
 }
}

Then I used a link like this to call it

<f:verbatim><a href="?exportToExcel">Export</a></f:verbatim>