网上的代码结合自己的修改写出了这个验证码生成工具类，只生成字符形式的。
import java.security.SecureRandom;import java.util.Random;/*** 验证码生成工具类*/public class VerifyCodeUtils {/*** 数字*/private static final char[] SYMBOLS_NUM = "0123456789".toCharArray();/*** 数字及大小写字母*/private static final char[] SYMBOLS_CHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();/*** 安全随机数*/private static final Random RANDOM = new SecureRandom();/*** 生成数字验证码** @param length 长度* @return 验证码*/public static String generateNum(int length) {return generateVerifyCode(length, true);}/*** 生成数字及大小写字母验证码** @param length 长度* @return 验证码*/public static String generateChar(int length) {return generateVerifyCode(length, false);}/*** 生成数字及大小写字母验证码** @param length 长度* @param onlyNum 是否只包含数字* @return 验证码*/private static String generateVerifyCode(int length, boolean onlyNum) {char[] lib = onlyNum ? SYMBOLS_NUM : SYMBOLS_CHAR;char[] nonceChars = new char[length];for (int index = 0; index < nonceChars.length; index++) {nonceChars[index] = lib[RANDOM.nextInt(lib.length)];}return new String(nonceChars);}}
