//循环内
for (int i = 0; i < 10; i++) {
StringBuffer sb = new StringBuffer();
int m = random.nextInt(9)+1;
do {
str=null;
for (int j = 0; j < m; j++) {
int n = random.nextInt(s.length()-1);
sb.append(s.charAt(n));
}
str = sb.toString();
} while (list.contains(str));
list.add(str);
//循环外
List<String> list = new ArrayList<String>();
String s = "0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";
Random random = new Random();
String str;
