LIFERAY PORTAL FORCE BROWSER TO ATTACH THE PDF INSTEAD OF AUTO OPEN IT

public StreamedContent getAttachment(){

          portletResourceResponse.setContentType("application/pdf");  //application/pdf
  portletResourceResponse.setProperty("Content-Disposition", "attachment");

    try{

 portletResourceResponse.flushBuffer(); OutputStream out =                portletResourceResponse.getPortletOutputStream();
 out.write(------);

 out.flush();
 facesContext.responseComplete();
 out.close();
 }catch(Exception e)
{
    e.printStackTrace();
}
 return null;
 }