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.
I've never done any http work with java but it seems to me that the site you are requesting https connection is missing or has expired SSL certificate. If you request webpage through https that has no SSL via browser the browser emits a warning. You can add an exception to that site if you want to, similarly (assuming that my first assumption about this exception is correct) you should be able to ignore this exception by putting the corresponding code in a try-catch block.