I guess the best way of achieving flexible and user friendly HTML layout it by using external JavaScript library, such as jQuery or mootools. The reason is - in traditional web frameworks after you send HTML content to web browser, server cannot manipulate with it. Also, I guess good principle is to use Java only for serving content, and using client-side framework to do all the magic with User Interface.
Moreover, You will find plenty of examples how to work with those libraries like this one.
If you would really like to stick to plain Java, since you might know anything about JavaScript, I suggest checking out Google Web Toolkit and Vaadin. You can write Java code almost without any restrictions, and it will be "converted" (compiled) to JavaScript automatically. But that decision should be considered deeply, since learning GWT or Vaading might be more time consuming and not always applicable.