Runtime.exec() not behaving as expected

You're splitting on spaces, and "1 2 3 4 5" has spaces in it.

I recommend passing it in delimited differently. I would use semicolon (;) or any non-volatile delimiter. and split the string that way. The thing to remember here is you do not care about what gets passed into your program only what you are willing to execute. Therefore your cmdLine variable should look like this:

--user-agent; "1 2 3 4 5"; --dump-header;

use String.trim() as necessary.