Your solution has a time complexity of O(n log(n)), and that is not good.

A naive solution can be done in O(n), checking all the elements checking for the minimum, and the best solution can be done using a modified binary search (check the editorial of this problem).

I am not familiar with Java. (So, if I am wrong, never mind.)
But I have a question about your solution.
Consider the following test case:
[1,2,2,2,3] or [3,2,2,2,1]
Although you sorted the array, but the majority element is not the first one. Am I right?