jsowell-charger-web/jsowell-common/src/main/java/com/jsowell/common/util/RandomUtil.java

package com.jsowell.common.util;

import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

import java.security.SecureRandom;
import java.util.List;
import java.util.Random;
import java.util.Set;

/**
 * 获取随机数的工具类
 */
public class RandomUtil {
	private static final String SYMBOLS_NUM = "0123456789"; // 纯数字
	//如果需加入字母就改成0123456789abcdefg...........
	private static final String SYMBOLS_NUM_ALPHABET = "abcdefghijklmnopqrstuvwxyz0123456789";

	private static final Random RANDOM = new SecureRandom();

	/**
	 * 获取6位的短信验证码 纯数字
	 *
	 * @return 随机数字
	 */
	public static String getSMSVerificationCode() {
		return getRandomNumber(6);
	}

	/**
	 * 获取指定长度随机数
	 *
	 * @param length 需要的长度
	 * @return 随机数
	 */
	public static String getRandomNumber(int length) {
		char[] nonceChars = new char[length];  //指定长度，自己可以设置
		for (int index = 0; index < nonceChars.length; ++index) {
			nonceChars[index] = SYMBOLS_NUM.charAt(RANDOM.nextInt(SYMBOLS_NUM.length()));
		}
		return new String(nonceChars);
	}

	/**
	 * 获取一组不重复的6位数随机数
	 *
	 * @param num 数量
	 * @return
	 */
	public static List<String> getRandomNumberList(int num) {
		List<String> list = Lists.newArrayList();
		for (int i = 0; i < num; i++) {
			String code = getNotRepeatCode(list);
			// System.out.println(code);
			list.add(code);
		}
		return list;
	}


	/**
	 * 获取一组不重复的6位数随机数
	 */
	private static String getNotRepeatCode(List<String> list) {
		// 获取随机验证码
		String code = RandomUtil.getSMSVerificationCode();
		// 判断list中是否存在
		boolean contains = list.contains(code);
		if (contains) {
			// 已经存在，重新获取一个
			code = getNotRepeatCode(list);
		}
		return code;
	}


	public static void main(String[] args) {
		List<String> randomNumberList = getRandomNumberList(100000);
		Set<String> set = Sets.newHashSet(randomNumberList);
		System.out.println("list长度：" + randomNumberList.size());
		System.out.println("set长度：" + set.size());
	}

}