Joshua Allen -- the season 4 winner of "So You Think You Can Dance" -- faces serious time behind bars after allegedly attacking his girlfriend twice in a 2-month span.
According to the D.A.'s Office ... Allen went after his girlfriend last month, chasing her inside a coffee shop when she tried to run away. When a woman tried to step in, Allen allegedly threw a glass vase at her and vandalized the shop before bystanders took him down.
He also strangled her in April, according to the D.A. At the time, she already had a criminal protective order against Allen for a prior domestic violence conviction.
Allen's been charged with 2 felony counts of willfully injuring his girlfriend, 1 felony assault with a deadly weapon ... and 4 misdemeanors related to battery, vandalism and violating the protective order.
If convicted ... he faces more than 10 years in prison.