随机数生成a-z，0-9

import java.util.Random;

public class RandomUtil {

    public static String getRandomString(){
        int length = 15;//定义长度
        String base = "abcdefghijklmnopqrstuvwxyz0123456789";//取值范围：a-z,0-9
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        //循环生成随机数
        for (int i = 0; i < length; i++) {
            //在base字符串长度范围内随机生成一个int随机数,作为索引
            int number = random.nextInt(base.length());
            //根据索引获得base字符串对应位置的值，将值添加到字符串中
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }

    //测试
    public static void main(String[] args) {
        String rs = getRandomString();
        System.out.println(rs);//j65jl0ssh1raiyd
    }
}