Meek Mill -- Judge Revokes Parole ... 3-6 Months in Philadelphia Lockup

Rapper Meek Mill crossed the line one time too many with the D.A., and now he's sitting in a Philadelphia jail ... where he'll remain for the next several months.

Meek was in court this afternoon to face the judge for multiple violations of his parole on a 2009 drug and gun conviction. Meek's been bad-mouthing the District Attorney's Office on Twitter. Prosecutors say he also repeatedly scheduled concerts without getting them pre-approved -- and changed his mobile phone number without telling them.

Today in court ... the judge told the rapper, "I didn't want to do this, but you made me do this" -- and then he was sentenced to 3 to 6 months in a city jail.

Sources in Meek's entourage tell us the rapper thinks the D.A. had a vendetta against him, and wanted to take him down because he has an album dropping in September.

Meek begged the judge for mercy, saying ... "This will be extremely damaging to my life."