This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
If you had asked "What types of listeners are there?" I would have pointed you to the servlet javadocs, where they are listened. But as it is I'm not making sense of the question. Are you asking how many listeners you can use in a web app? That's not part of the servlet spec; it's probably limited by available memory, but can't really be what you're asking.