Butterworth low pass filter Java code

Apply Butterworth low pass filter with an appropriate order and cutoff frequency (you choose) to the above three images. Present the Fourier spectrum (log magnitude) and filtered images in your report and discuss the effect of this filter on the above three images including the effect of the cutoff frequency.

The above three images don't matter, I just need a Java code, or even psuedocode on how to implement a Butterworth low pass filter to an image.