Here is my first screensaver:
http://www.croftsoft.com/library/software/savor/
Here is the source code:
http://croftsoft.cvs.sourceforge.net/croftsoft/apps/src/com/croftsoft/apps/savor/Savor.java?view=markup
It is Open Source:
http://www.croftsoft.com/library/code/
It is based on the SaverBeans Screensaver SDK version 0.2:
https://jdic.dev.java.net/documentation/incubator/screensaver/