1.验证码就是将大小写字母和数字放入到集合中，使用Collections.shuffle(list);将list集合中的数据进行打乱，遍历集合，对集合中的字符进行sb.append()操作，最后对sb进行下表截取 String result = afterShuffle.substring(5, 9);

代码

public class GenerateWord {

    public static void main(String[] args) {

        timer2();

    }

    // 第二种方法：设定指定任务task在指定延迟delay后进行固定延迟peroid的执行  

    // schedule(TimerTask task, long delay, long period)  

    public static void timer2() {

        Timer timer = new Timer();

        timer.schedule(new TimerTask() {

            public void run() {

                String[] beforeShuffle = new String[] { "2", "3", "4", "5", "6", "7", "8", "9", "A",

                        "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P",

                        "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z","a","b","c","d","e","f","g","h","i","g","k" };

                List<String> list = Arrays.asList(beforeShuffle);

                Collections.shuffle(list);

                StringBuilder sb = new StringBuilder();

                for (int i = 0; i < list.size(); i++) {

                    sb.append(list.get(i));

                }

                String afterShuffle = sb.toString();

                String result = afterShuffle.substring(5, 9);

                System.out.println("验证码" + result);

            }

        }, 1000, 1000);

    }

}