Both Java and Perl can perform well. That said, a lot depends on what sort of processing you'd need to do; in particular, whether your workload's CPU-bound or IO-bound.

Personally I'd recommend Perl; it's flexible, it'll allow for a rapid development cycle, and text processing is one of its major strengths. (That said, I'm hardly neutral, and this is PerlMonks, after all.)

If performance is so critical, it might also pay to measure rather than guess: give both languages a try, and see which performs better.

Also, the search box on this site is your friend! Give it a try, you'll find nodes like Perl and Java comparison and others that may be helpful. :)