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.
Java-based tutorials and books will probably involve a framework like JXTA. It doesn't make sense to reinvent the wheel, unless, of course, this is an academic exercise. Google turned up one P2P article that doesn't rely on a framework.