Get random location within radius

A feature in the plugin I'm developing includes spawning a chest on the surface at a random location. The issue is that the location must be within a 250 block radius from the world spawn.

Is there a formula of some kind that would accomplish this task? How would go about this?

 

Code:java

 
Location startFrom;
Location output = startFrom.clone();
output.add((random.nextBoolean() ? 1 : -1) * random.nextInt(radius),
(random.nextBoolean() ? 1 : -1) * random.nextInt(radius),
(random.nextBoolean() ? 1 : -1) * random.nextInt(radius)); 
return output;
 

triangular distrubution code:

Code:java

 
Location startFrom;
Location output = startFrom.clone();
output.add(random.nextInt(radius) - random.nextInt(radius),
random.nextInt(radius) - random.nextInt(radius),
random.nextInt(radius) - random.nextInt(radius)); 
return output;
 

 

Brilliant! Thank you very much!

 

Whats the difference between the two? Also seems that the y changes as well..

 

the first 1 have sqaure distribution, the second triangulair

 

Is the below graphic correct?

For future people who stumble upon this.. Here is a graphic to help you understand..