how can i make strawberry jam that will last for years in the cupboard?

Make the jam as you would normaly, fill up the sink with cold water and leave them in there. It's the same effect as a fridge

I made damson jam under the same conditions and I used kilner jars for storage. I put the jam in whilst still hot, cut a disk of greaseproof paper to fit. poured a desert spoon full of hot lard over the jam making sure that the jam surface was covered, placed the disc of greaseproof on top and finally put a desert spoon full of spirit on top. I used brandy and then sealed the jar. I placed the full jars in a cupboard and the last one was used some ten years later and there was not a vestige of mould in any of the jars.

cook it down til it is really thick and dry or dehydrate it into fruit leather, this will keep quite a long time.

cook it down and put it in canning jars and seal with paraffin (wax)

http://www.pickyourown.org/jam.htm