Rearranging numbers of an array like a wave
Few observations.


You don't need to maintain swap2 separately, it is always swap1 + 1, so can be simply declared inside the loop's body.
Your boundaries check inside the loop body is redundant, loop condition alone is enough.
You're probably performing too many int-to-Integer and back conversions. Even more, the question deals with arrays, you don't need to pre-convert the argument into a list. Accept, process and return an array of plain ints.