Upload: use Servlet 3 API when supported

[ebruchez]

See #985 for background information.

The idea here is that the container has the ability to close the connection. But this has to be verified, at least with Tomcat.

A quick glance at Tomcat sources seems to indicate that a file upload, when swallowAbortedUploads is set to false (which is not the default!), will promptly close the connection. See Request.java as a starting point.

In short:

• using Tomcat 7
• with swallowAbortedUploads is set to false
• and Orbeon Forms using the Servlet 3 upload API

would be an improvement over the current situation, where the connection cannot be closed.

Drawbacks:

• support for pre-Servlet 3 containers
• does not resolve handling non multipart large request bodies (like a POST to a service)

[ebruchez]

Servlet 3.0 API is no longer an issue as it is now many years old and widely supported.