java代碼獲取指定長度隨機數

/**
* 獲取指定長度隨機數
* @param len
* @return
*/
public static String getRandom(int len){
Random r = new Random();
int bitNum=1;
for(int i=0;i<len;i++){
bitNum=bitNum*10;
}
        long num = Math.abs(r.nextLong() % (bitNum));
        String s = String.valueOf(num);
for (int i = len - s.length(); i >0 ;i--) {
s = "0" + s;
}
        if(s.length()>len){
s=s.substring(0,len);
        }
        return s;
    }