随机生成验证码

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import java.util.Random;   /**  * 随机生成验证码工具类  */ public class ValidateCodeUtils {     /**      * 随机生成验证码      * @param length 长度为4位或者6位      * @return      */     public static Integer generateValidateCode(int length){         Integer code =null;         if(length == 4){             code = new Random().nextInt(9999);//生成随机数，最大为9999             if(code < 1000){                 code = code + 1000;//保证随机数为4位数字             }         }else if(length == 6){             code = new Random().nextInt(999999);//生成随机数，最大为999999             if(code < 100000){                 code = code + 100000;//保证随机数为6位数字             }         }else{             throw new RuntimeException("只能生成4位或6位数字验证码");         }         return code;     }       /**      * 随机生成指定长度字符串验证码      * @param length 长度      * @return      */     public static String generateValidateCode4String(int length){         Random rdm = new Random();         String hash1 = Integer.toHexString(rdm.nextInt());         String capstr = hash1.substring(0, length);         return capstr;     } }