Updating certain values in text file
You could simplify with Regular Expressions:

Pattern pattern = Pattern.compile("log-(\\d+)sr");
Matcher matcher = pattern.matcher(input);
StringBuffer buffer = new StringBuffer();
while(matcher.find()) {
  Long value = Long.parseLong(matcher.group(1), 10);
  Long increased = value + 100;
  matcher.appendReplacement(buffer, increased.toString());
}
System.out.println(buffer.toString());