what is the difference between the use of will and be going to

WILL
1. rapid/spontaneous decision
- I'm hungry. I will eat.
2. offer
- That looks heavy. I will help you with that.
3. promise
- Don't worry, I will be there.
4. threat
- I will tell your mother if you don't stop.
5. refusal
- I won't accept it.

GOING TO
1. prior plan (i.e. the decision was made before the moment of speaking)
- I am going to Jakarta. I have bought the train ticket.
2. evidence/signs
- It's 7-0. They are going to win.

NOTE : for making predictions, both WILL and GOING TO can be used.
- It is going to/will rain tomorrow