How do you force a download prompt, before data it sent from a servlet?

Question

Hi all,

How do you force a download prompt to popup before you send any data to browser? I know about content disposition attachment, but this is different. Basically, the servlet starts sending data to the client, and then the client open a dialog, open, save, cancel.

The probably is my servlet is slow getting the data, and it gets all the data in memoery before it sends any thing to the client. I would like to do something to trigger the dialog, before I am ready to send the data. Otherwise, the browser just waits there, like you did nothing.

I want to trigger that save dialog sooner. I can't send data, because the data is not ready.

Any ideas?

Grae

Answer 1

You can simply use the OutputStream and send data over it. This way you don't have to get the whole data in memory.

---

On the same topic :

• Streaming large files in a java servlet

Answer 2

If you want your app to appear more responsive to the user (and prevent multiple clicks on the download link) consider to make the link point to a location (servlet or JSP) which does nothing but issue a 301/302 redirect with a reponse body, i.e. an HTML page displaying a message asking the user to be patient while the data is collected. The redirect's location should then point to your servlet which delivers the download.