I hear that lemon essential oil works great too. Sometimes just soaking the jar in water overnight does the trick too.
My trick to remove glue residues from jars after peeling the label off is peanut butter! It is super easy! All I do, is just lather on peanut butter on the residue area and let it sit overnight or maybe about 12 hours. After, wash in hot soapy water as one would normally wash dishes. With rubbing, the oil in the peanut butter will remove the glue. I find with really thick residue, it needs to be done another time. Sometimes, for what ever reason, the residue does not come off. I may have 2 jars I have been unable to clean up.