[logback-user] FileAppender and flushing

In a very simple intro-style prototype using logback, I've got a rolling file appender logging correctly to a file. However, I don't see the log lines immediately; however, they do show up when I close my java app. This means things are getting buffered. But I can't find something like Logger.flush() or any flush method as a work my way back up the inheritance tree. How do I ensure immediate flushing? Thanks.