Java生成4位或者6位验证码的工具类

public class RandomUtils {

	private static final Random random = new Random();

	private static final DecimalFormat fourdf = new DecimalFormat("0000");

	private static final DecimalFormat sixdf = new DecimalFormat("000000");

	public static String getFourBitRandom() {
		return fourdf.format(random.nextInt(10000));
	}

	public static String getSixBitRandom() {
		return sixdf.format(random.nextInt(1000000));
	}

	/**
	 * 给定数组，抽取n个数据
	 * @param list
	 * @param n
	 * @return
	 */
	public static ArrayList getRandom(List list, int n) {

		Random random = new Random();

		HashMap<Object, Object> hashMap = new HashMap<Object, Object>();

		// 生成随机数字并存入HashMap
		for (int i = 0; i < list.size(); i++) {

			int number = random.nextInt(100) + 1;

			hashMap.put(number, i);
		}

		// 从HashMap导入数组
		Object[] robjs = hashMap.values().toArray();

		ArrayList r = new ArrayList();

		// 遍历数组并打印数据
		for (int i = 0; i < n; i++) {
			r.add(list.get((int) robjs[i]));
			System.out.print(list.get((int) robjs[i]) + "\t");
		}
		System.out.print("\n");
		return r;
	}
}