HtmlUnit is a pretty decent scriptable browser. I use it for developing alot of website scrapers and various bots. By default, the logging to the standard output stream is pretty verbose. A quick way to disable it programmatically is to add the following static initializer to your code:
static {
LogFactory.getFactory().setAttribute("org.apache.commons.logging.Log", "org.apache.commons.logging.impl.NoOpLog");
}