A simple approach is:

String zeroTo255 = "(\\d{1,2}|(0|1)\\d{2}|2[0-4]\\d|25[0-5])";
public String pattern = zeroTo255 + "\\." + zeroTo255 + "\\." + zeroTo255 + "\\." + zeroTo255;

1) \\d{1,2} catches any one or two digit number

2) (0|1)\\d{2} catches any three digit number starting with 0 or 1.

3) 2[0-4]\\d catches numbers between 200 and 249.

4) 25[0-5] catches numbers between 250 and 255.

Note that \d represents digits in regular expressions, same as [0-9]

Edit: Replaced "." with "\." as suggested in some of the comments