Full disclosure, I work on the team that write the Java tooling for TFS so take this answer as appropriately biased :-)
As far as TFS is concerned - all code is created equal. It's just bytes in files that it checks in to version control. Like all SCM systems it doesn't care what language the files are written in.
Microsoft provide a full, rich TFS Plug-in for Eclipse (called Team Explorer Everywhere). This provides full source control, work item tracking, build, sharepoint, reports access etc into TFS from Eclipse based IDE's. It's written in 100% Java and talks directly to the web services exposed by TFS.
In addition we also provide a cross-platform command line client for TFS so that you can talk to TFS from the command line on your operating system of choice (Mac, Linux, Solaris, HP-UX, Aix etc all fully supported).
Finally, if you have tools written in Java that want to talk to TFS then they can make use of the TFS SDK for Java which is the full API that we used to create the Eclipse integration and cross-platform command line client but packaged up with samples and snippets and ready for you to redistribute with your applications.
When it comes to build you have a couple of choices. If you want to stick with your current build server then it is likely that this already supports talking to TFS (all the popular open source build servers do). In addition to that, Microsoft provide the TFS Build Extensions which allow you to run Ant or Maven based builds on the Team Foundation Build server. The build results (along with any warnings or errors) are published back into TFS along with any JUnit test data if you execute JUnit tests as part of your build. Also you get to create and manage the build definitions in the Eclipse IDE and have one place to manage access to them etc.
So - the level of support for Java is very high and Microsoft has shown consistent investment in this area. We recently shipped some TFS 2010 Power Tools for Eclipse and we've also been shipping preview releases of Team Explorer Everywhere 11 alongside Team Foundation Server 11 (we're the same team inside the company).
To import history from SVN, that's the same as importing history from any SCM tool into TFS (or TFS into any SCM tool). You have a couple of options. You can take a snapshot and cut over at a particular point (such as a release) or you can migrate history. To Migrate history from SVN there are some partner solutions available including one from Timely Migration that I've seen a lot of customers have success with.
Hope that helps.
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