Re: Grails - J2ee integration
You could have your JSP webapp act as a proxy, accepting an AJAX request from the browser, then making a request to the Grails webapp, processing the response and forwarding that back to the browser.
Browser -> J2EE app -> Grails app
Browser <- J2EE app <- Grails app
this would get complicated if it required any cookies for the interaction with the Grails app.
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Stephen Souness