如何在Android中实现基于距离的类似火种的搜索？

I have started to develop an Android application where I need a distance based search. The user should be able to choose the maximum distance, let's say 3 km. I have already written some code where I get every user's current location (Lat, Lng) and store it in a mysql database. Then the app retrieves every user's position and finds the distance between the user and the other ones. With an if loop, the app checks if the value entered by the user is less or equal to each user distance.I have started to develop an Android applicatio