I want to do some functional testing on a (restful) webservice. The testsuite contains a bunch of test cases, each of which performs a couple of HTTP requests on the webserv
jUnit can't do that sort of thing -- though TestNG does have @BeforeSuite and @AfterSuite annotations. Normally, you get your build system to do it. In maven, there are the "pre-integration-test" and "post-integration-test" phases. In ANT, well you just add the steps to the task.
Your question is pretty much a dup of Before and After Suite execution hook in jUnit 4.x, so I'd take a look at the suggestions over there.