Here's a nice lay summary of Apache license.
...here's what the Apache license says in layman's terms:
It allows you to:
- freely download and use Apache software, in whole or in part, for personal, company internal, or commercial purposes;
- use Apache software in packages or distributions that you create.
It forbids you to:
- redistribute any piece of Apache-originated software without proper attribution;
- use any marks owned by The Apache Software Foundation in any way that might state or imply that the Foundation endorses your distribution;
- use any marks owned by The Apache Software Foundation in any way that might state or imply that you created the Apache software in question.
It requires you to:
- include a copy of the license in any redistribution you may make that includes Apache software;
- provide clear attribution to The Apache Software Foundation for any distributions that include Apache software.
It does not require you to:
- include the source of the Apache software itself, or of any modifications you may have made to it, in any redistribution you may assemble that includes it;
- submit changes that you make to the software back to the Apache Software Foundation (though such feedback is encouraged).
Judging from that, I'd say you need to include the license, do proper attribution, and leave the "prominent notices" if you change any Apache Commons libraries internals specifying what you changed. The license also has certain patent advantages as patent owners submitting contributions give you an implied patent license over them.