package com.test;

import java.util.Random;

public class TestRandom {

public static void main(String[] args) {
for (int i = 0; i < 1000; i++) {
System.out.println(new TestRandom().getRandomNUM(6));
}

}

public String getRandomNUM(int n){
String str = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; //62个字符
StringBuffer buffer = new StringBuffer();

for (int i = 0; i < n; i++) {
int ii = new Random().nextInt(62);// [0,61]
buffer.append(str.charAt(ii));
}
return buffer.toString();
}

}