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();    }}