By using innerHTML in jsp page which need to populate the data from database in to that page without refreshing that.
The whole premise of pushlets is to refresh data without refreshing the page.
In the past, I've implemented a remote scripting-ish solution using a hidden frame. People might argue with this approach and it's inherent difficulties, however it is up and working on a Fortune 500 companies site and has passed all their regression tests.
Hope that helps to get you started!