产生定义字符中随机数

public class RandomFileName {
?/**
? * 产生一个随机的字符串
? *
? * @param 字符串长度
? * @return
? */
?public static String getRandomString(int length) {
??String base = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
??Random random = new Random();
??StringBuffer sb = new StringBuffer();
??for (int i = 0; i < length; i++) {
???int number = random.nextInt(base.length());
???sb.append(base.charAt(number));
??}
??return sb.toString();
?}

?public static void main(String[] args) {
??System.out.println(RandomFileName.getRandomString(5));
?}
}