I would say the biggest threat to Java is Oracle themselves.
"Perhaps the final straw was what Gosling said was Oracle's move to rein him in. indeed they owned Sun and thus Java, so they also owned its creator and his intellectual property, so it was up to Oracle to decide what Gosling or anybody else had to say about Java."
http://www.eweek.com/c/a/Application-Development/Java-Creato...