数字与字母 随机数小demo

public String generateRandomId(){
        String chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ";
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < 16; i++) {
            buffer.append(chars.charAt(new Random().nextInt(chars.length())));
        }
        buffer.insert(0, "TR");
        return buffer.toString();
    }