Can't say for sure but it probably is really boring. I know I would go stir crazy just after a few days of being locked up in jail.
I couldn't imagine being locked up for a year or more in jail.
Although people who're sentenced for longer than one year will be sent to a prison which I hear is much better than regular jail with a bit more freedom to roam about and more things to do.
I don't want to ever experience it and I plan to stay away from jail and prisons.