Open source Projects for Java juniors

Hello guys. I am a java guy who have a decent knowledge and understanding of J2SE, and after a while I have noticed that to be really good at programming in java , it will be better to join an open source project that is implemented using Java. So, here I am seeking an advise for a java open source project which i can join to give me expertise in Java and programming in general and also give a hand to that great community. I would really prefer open source projects that still in the first phase and also that us using some Agile methodologies. That is it and Thanks in advance.