What you've done here could improve the overall security of the solution somewhat, but won't necessarily prevent session hijacking.
the security issue with placing the session ID in the URL is that URLs are exposed in various places (eg, copy and pasted URLs could expose a live session, URLs can be stored in proxy server logs, web server logs and browser history), which could allow an attacker to grab a valid session ID and get access to your users data.
Ideally you should remove the JSESSIONID from the URL in all places, and only use cookie storage.
Additionally if you want to mitiate Session hijacking there's a number of other areas to consider.
You need to use SSL on all pages where the session ID is passed (this is to mitigate the risk of the session ID being intercepted in transit (eg, the Firesheep attack).
If the session ID is set before you authenticate the user, you should ensure that a new session ID is issued when the user logs in.
Also if possible the session cookies should be use of the httpOnly and secure flags, to reduce the risk of them being leaked over cleartext channels.
There's some good additional information on the OWASP Site
BTW if you've got more question on the security side of things, there's a stack exchange site specifically for that at Security.stackexchange.com
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