If you really want to automate browser-based interactions, you could go further and use Watij, which runs a browser via the JVM and is driven via a browser-based API (I.e. you identify the button you want to press and it will actually do this)
Otherwise a library like the one you've identified will normally work. You have to watch out for client-side JavaScript interactions driving the requests, and configure proxies etc (I suspect this is your problem in the above)