The bar exam is a part of the hiring process, its just that its outsourced to a licensing agency. In the software field, each company just does it themselves.
Most large firms draw their entry-level associates from their pool of summer interns, which they hire two years before they graduate law school and take the bar exam. They also usually give people a mulligan on failing the bar exam the first time, so people might work somewhere for 6+ months before passing the bar.