Sometimes you want to copy a webpage to your computer. It can be as easy as
using the save button in your web browser. But what if you want to copy many
files automatically to your computer? Example, you want to download a set of
lecture notes with link
http://www.charlesli.org/java/articles/copyURL/test/note1.txt
.... http://www.charlesli.org/java/articles/copyURL/test/note100.txt.