随机数工具类

package com.JUtils.math;

import java.util.Random;

/**
 * 随机数工具类
 *
 */
public class RandomUtils {
    private static final String ALL_CHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String LETTER_CHAR = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String NUMBER_CHAR = "0123456789";

    /**
     * 获取定长的随机数，包含大小写、数字
     *
     * @param length
     *                 随机数长度
     * @return
     */
    public static String generateString(int length) {
        StringBuffer sb = new StringBuffer();
        Random random = new Random();
        for (int i = 0; i < length; i++) {
                sb.append(ALL_CHAR.charAt(random.nextInt(ALL_CHAR.length())));
        }
        return sb.toString();
    }

    /**
     * 获取定长的随机数，包含大小写字母
     *
     * @param length
     *                 随机数长度
     * @return
     */
    public static String generateMixString(int length) {
        StringBuffer sb = new StringBuffer();
        Random random = new Random();
        for (int i = 0; i < length; i++) {
                sb.append(LETTER_CHAR.charAt(random.nextInt(LETTER_CHAR.length())));
        }
        return sb.toString();
    }

    /**
     * 获取定长的随机数，只包含小写字母
     *
     * @param length
     *                 随机数长度
     * @return
     */
    public static String generateLowerString(int length) {
        return generateMixString(length).toLowerCase();
    }

    /**
     * 获取定长的随机数，只包含大写字母
     *
     * @param length
     *                 随机数长度
     * @return
     */
    public static String generateUpperString(int length) {
        return generateMixString(length).toUpperCase();
    }

    /**
     * 获取定长的随机数，只包含数字
     *
     * @param length
     *                 随机数长度
     * @return
     */
    public static String generateNumberString(int length){
        StringBuffer sb = new StringBuffer();
        Random random = new Random();
        for (int i = 0; i < length; i++) {
                sb.append(NUMBER_CHAR.charAt(random.nextInt(NUMBER_CHAR.length())));
        }
        return sb.toString();
    }

}