How can I replace ^I into tab spaces in vim editor for .java file?

When I open my .java file in vim, I could see a couple of lines prefixed with one / more ^I characters. It looks like tabs in Eclipse that has got converted into ^I. I would like to replace a single ^I into spaces with 4 characters. E.g ^I^I^I^IList rulePackagesHistory = result.getHistory(); How can do that in vim editor?