How to find the latter half of a pattern?

I'm trying to find the latter half of patterns of the following template:

foo/BAR 

'BAR' is the one I'm trying to retrieve. I tried with something like:

\b(foo)/([a-zA-Z]+)

This works fine, but this also matches http://foo/BAR - which I don't want.

I also tried

\\s(foo)/([a-zA-Z]+)

but this doesnt match when the line starts with foo/BAR. (I'm using java.util.regex)

(^|\s)foo/([a-zA-Z]+)

If you define a full "foo/BAR" token as both preceeded and followed by whitespace (or begin/end of the line)

I.e. it would find "abc", "XyZ", and "def" in

"foo/abc 123 hhh foo/XyZ http://foo/BAR foo foo/ foo/ghi% foo/def"

then you want

(?:^|\s)foo/([a-zA-Z]+)(?:$|\s)

\b is a word boundary, ^ is a start of line marker

^foo/(\w+)

How about

^(foo)/([a-zA-Z]+)

or

(?<!http://)(foo)/([a-zA-Z]+)