java 랜덤Key 값 생성

기본 10자리로 만들어 보았음
public static String randomKey(int length) {
StringBuffer result = new StringBuffer();
Random rnd = new Random();

int size = 10;
if(length > 0) {
size = length;
}

for (int i = 0; i < size; i++) {
    int rIndex = rnd.nextInt(3);
    switch (rIndex) {
    case 0:
        // a-z
    result.append((char) ((int) (rnd.nextInt(26)) + 97));
        break;
    case 1:
        // A-Z
    result.append((char) ((int) (rnd.nextInt(26)) + 65));
        break;
    case 2:
        // 0-9
    result.append((rnd.nextInt(10)));
        break;
    }
}
return result.toString();
}