Jumping does not indicate bad temperament: Think about this. When the GSD was a little puppy and a cute fur ball, he jumped on people. Immediately people thought it was cute, picked him up and petted him. So the little fellow thinks "Jumping is good. I get people to pet me. I will always do this. yay!". Then before you realize it, the little fur ball has become a 30kg dog. But he still thinks "Jumping is good. People love me". So it is not really his fault. He is just trying to get some love :)
I myself have a boxer. Boxers are known to be jumpers. So she cannot help jumping. I have tried several methods. But one method has been the fastest, most effective and most humane to the dog.
Step 1: Teach the dog you don't like him when he jumps. When he jumps, just fold your hands and turn around. If you observe, when puppies jump on grown dogs, grown dogs to the same. They just turn around. Dog will immediately stop jumping. No dog likes being ignored when he is trying to get attention.
Step 2: Reinforce this behaviour. Tell EVERY PERSON the dog meets to do the same if the dog jumps. Soon he will realize "jumping is not good. No one loves or pets me when I jump".
Remember that he is jumping to get attention. Yelling or interacting with him in any ways is giving him attention. So he will continue jumping. Give him attention and love only AFTER he calms down.
Patience is the key. Over several months or years, people have been giving him attention, making him feel that jumping is good. He cannot unlearn that in days. Give him a little time. He WILL learn his new lesson - "Jumping is bad! No one gives me love when I jump"