Problems 2.3 in Peskin's book

Question

It's about how to evaluate the integral below, $$ D(x-y)=\int \frac{d^3 p}{(2\pi)^3}\frac{1}{2\sqrt{p^2+m^2}}e^{-i\vec p\cdot (\vec x-\vec y)} $$ it describes the amplitude for a scalar particle in free Klein-Gordon field propagating from y to x (y and x have a space-like interval) . The book said that the result can be written explicitly in terms of Bessel function but I have not idea at all.