Options for Migrating Java Swing Application

I have a large java swing desktop application that communicates over web services to an ASP.NET based server with a SQL database. My desire is to have a web based (html) application. What options do I have for preserving my java code that isn't ui specific? (i.e. all my services and business logic, not my swing specific code)

I thought of porting my java ui code to Spring MVC and then having the spring server serve up the web pages and communicate to the asp.net server. I'm leery of that option because I would then have two server technologies for the same web application.

I also considered rewriting the UI as a ASP.NET MVC web application as well as rewriting the server in a java based technology.

Ultimately, I know there is throw-away code here but I'm looking for options that would allow me to keep much of my java code that isn't ui/swing specific.

Ideas?