Java随机输出验证码包含数字、字母、汉字

//随机验证码，有数字、字符
//生成随机数，然后再截取，还要限定随机数的范围
String zimu = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890" ;
Random rm = new Random();    //生成随机数

int a = rm.nextInt(61);        //0到61之间的随机数赋值给a
int b = rm.nextInt(61);
int c = rm.nextInt(61);
int d = rm.nextInt(61);

char zf = zimu.charAt(a);    //将数组中索引为a的字符赋给zf
char zd = zimu.charAt(b);
char zc = zimu.charAt(c);
char zq = zimu.charAt(d);

System.out.println("请输入验证码： "+ zc +" " + zf +" " + zq +" " + zd);