Building Applications - eXist: A NoSQL Database and Application Development Platform - page 211

The session Extension Module
A session represents the interaction with a server for a specific client over a period of
time. You may store data in the session that is available across requests for the same
client. Each client may have a distinct session with the server. A session is accessed
with the session extension module. This module is really just a very simple XQuery
wrapper around the underlying HttpSession Java class that eXist handles for you.
Some usage hints:
• A session must be created with the session:create function. Lots of other func‐
tions that do something with a session create it implicitly for you, but it can
never hurt to create it explicitly with session:create . If the session already
exists, the call is ignored.
• A session can hold attributes that are name/value pairs. Attribute values can be
anything from simple strings to complex XML fragments. Use the functions
session:set-attribute and session:get-attribute to work with these.
• Sessions invalidate automatically after not being accessed for a certain amount of
time. You can control this interval using the session:get-max-inactive-
interval and session:set-max-inactive-interval functions.
The response Extension Module
You control the response to a request via the response extension module. This mod‐
ule is really just a very simple XQuery wrapper around the underlying
HttpServletResponse Java class that eXist handles for you. Useful functionality here
includes:
• Setting cookies with the response:set-cookie function
• Explicitly setting response headers and the overall status code with the
response:set-header and response:set-status-code functions
• Redirecting the client to another page with response:redirect-to
• Streaming data directly to the output with the response:stream and
response:stream-binary functions (useful for creating download functionality,
as described next)
Creating “download XML file” functionality
Creating a download function for an XML file, in which the browser asks you where
to store it instead of displaying it, is not as easy as it may sound. You have to trick the