Where does the term Cup O Joe Come from?

I recently got an e-mail from someone who asked me that question.
I had an idea in the back of my mind. How it got there I don't know. But before I responded with this answer, I did about 10 minutes of research on the web. Ask Jeeves was a dead end. But I have a dictionary site listed on my favorites - http://www.onelook.com/ . An excellent source and the place where I found an answer.

OneLook listed The Word Detective
http://www.word-detective.com/041899.html#joe

(here's the info from the source)
Meanwhile, back at your question, there is, alas, no definitive answer to the riddle of "joe" as slang for coffee, which first appeared around 1930. It may be a variant of "java," also a popular term for coffee since the 19th century, when the island of Java in Indonesia was a major source of the world's coffee. Another theory holds that "joe" comes from the title of the once very popular Stephen Foster song "Old Black Joe."
Yet another theory, and one that rings true to me, is that "joe" as slang for coffee might be derived from "Joe" as a synonym for "the common man," as in "regular joe." This use of "Joe" as a generic name for the man in the street dates back to around 1911 and was very widespread in the military services, as in "G.I Joe," which was slang for the common soldier long before it became the name of a toy. Since "joe" as slang for coffee was and is especially common in the Navy, and since the Navy pretty much runs on coffee, it seems logical that the military slang term for an average guy could have been extended to the average guy's usual beverage.

This last theory was the one I had in the back of my head. My dad was a Joe (his real name) and he drank some cup o joe, he did his spint in WWII, he was a regular guy, a regular Joe.

More Good Coffee Ramblings at
www.good-coffee.cup-o-joe.com

Happy Sipping,
John Dog, Eccentric Outsider Artist