Joshua Allen -- the Season 4 winner of "So You Think You Can Dance" -- was sentenced to 1 year behind bars for attacking his girlfriend ... TMZ has learned.
Allen pled no contest Thursday to felony domestic violence and felony assault with a deadly weapon. He was then taken directly to jail. Allen wept in court after he was sentenced.
He also got 5 years probation and was ordered to complete 52 weeks of domestic violence classes. He can't go near the victim for a decade.
TMZ broke the story ... Allen went after his gf back in June and chased her into a coffee shop. When a woman tried stepping in, Allen allegedly threw a glass vase at her and trashed the shop before bystanders took him down.