Primefaces Document Viewer Exception Handling - jsf

Question

I am using Primefaces documentViewer from primefaces-extensions 12 as follows :
<pe:documentViewer zoom="page-fit" pagemode="thumbs"
id="iframeViewPdf" width="80%" height="800"
url="/pdfServlet?id=#{param.id}"/>
My controller writes the bytes to the response as follows :
#RequestMapping(value = "/pdfServlet")
public void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
// code here
try{
documentId = request.getParameter("id");
inputStream = myRepository.getFileAsInputStream(documentId);
outputStream = response.getOutputStream();
IOUtils.copy(inputStream, outputStream);
}catch(Exception e){
// all below didn't work
// request.getRequestDispatcher(request.getContextPath() + "/error").forward(request, response);
// response.sendRedirect(request.getContextPath() + "/error");
// throw e;
// what should be done here to redirect to error page / show error message in the page
}finally{
IOUtils.closeQuietly(inputStream);
IOUtils.closeQuietly(outputStream);
}
}
Above code works fine, but when any exception occurs in the backend I want to handle it in the client side, I tried to throw the exception in the catch part and got no effect.
Note: my application has error page configuration for any exception to forward to error page.
I also tried to redirect/forward to error page in the catch part, but I always gets an exception that cannot forward/redirect after response is committed.
How can I better handle exception in this case?
UPDATE : below is the response I get in the viewer when loading exception occurs in the backend, is there's any way to call a javascript function instead ?

Answer 1

I was able to handle the error using javascript interval on load as follows :
window.onload = function(){
PF('statusDialog').show();
var checkExist = setInterval(function() {
var iframe=document.getElementsByTagName('iframe')[0];
var innerDoc = iframe.contentDocument || iframe.contentWindow.document;
var viewer = innerDoc.getElementById('viewer');
var errorMessage = innerDoc.getElementById('errorMessage');
var innerHTML = viewer.innerHTML;
if(innerHTML != null && innerHTML!='' && innerHTML!='undefined'){
clearInterval(checkExist);
PF('statusDialog').hide();
}
if(errorMessage != null && errorMessage.innerText != ''){
clearInterval(checkExist);
PF('statusDialog').hide();
// handle error here
window.location.href = getContextPath()+'/error';
}
}, 1000);
}

Answer 2

Why not put a custom Error in your web.xml???
web.xml
<!-- Handle Invalid PDF errors gracefully -->
<error-page>
<exception-type>com.your.InvalidPdfException</exception-type>
<location>/pages/error.xhtml</location>
</error-page>
Then in your code throw new InvalidPdfException().