First what do you know best, and will that work?

I like Perl because it has regex. I'm not sure of the native regex support for Java. And Perl is SUPER fast on large text files.

I've read and looked for keys, line by line, in a 500,000 line file from Excel (saved to tab-delimited). It took about 3-5 seconds. Your 1GB files should not be a problem unless you're on a real old server or PC with less memory.