Links for Studying Servlets

hi,
I am posting some good links for going through servlets

http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
http://www.novocode.com/doc/servlet-essentials/
http://java.sun.com/products/servlet/2.3/javadoc/
http://java.sun.com/javaee/5/docs/tutorial/doc/

check them out...............