I have exactly the same problem with an apple tree bought last year and which produced a crop for me. It has blossomed this year, but no apples are developing. I saw an apple grower interviewed on the TV News, and he said it is a disastrous year for fruit. Long established apple trees that he usually gets about 500 apples from will only be bearing about 50 apples each this year. All down to the spring we had, according to him. The wrong weather when the blossom was out meant a lot of it was destroyed, and not enough pollinating insects at that time either.
Now I am sure some gardeners will add to this thread that they are having a bumper crop of apples and plums!