前言：以前做过的一个项目，刚开的时候始验证码是在前端生成前端验证的，后来觉得不靠谱，另外就是找回密码的功能也需要发送邮件和短信的验证码，所以，验证码就必须在后端生成并且保存到应用会话中才行了！所以，就有了下面的这段简单的代码，这段代码虽然简单，但也是生成验证码的一种思路，在此小记一笔以备后用。
1：如下是生成验证码、测试生成验证码的方法，比较简单，注释也比较清楚，不多说了
package start;
import java.util.Random;
public class HelloMain {
/**
* 主函数，作为调用和测试生成验证码方法的入口
* @param args
*/
public static void main(String[] args)
{
for(int i=0; i<10;i++)
{
System.out.println("【"+i+"】"+" 【the verification code is】 "+createVerificationCode(6));
}
}
/**
* 生成指定长度的验证码
* @author Q
* @param verificationCodeLength
* @return String
* @since 2016-09-6
*/
public static final String createVerificationCode(int verificationCodeLength)
{
// 所有候选组成验证码的字符，可以用中文
String[] verificationCodeArrary={"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z",
"A","B","C","D","E","F","G","H","I","J", "K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"
};
String verificationCode = "";
Random random = new Random();
//此处是生成验证码的核心了，利用一定范围内的随机数做为验证码数组的下标，循环组成我们需要长度的验证码，做为页面输入验证、邮件、短信验证码验证都行
for(int i=0;i<verificationCodeLength;i++){verificationCode += verificationCodeArrary[random.nextInt(verificationCodeArrary.length)];}
return verificationCode;
}
}
2：如下是运行主函数生十组六位长度验证码的运行结果演示图
3：小结
此例的核心和JS-改变页面的颜色之变化核心-获取六位的随机数类似，都需要利用随机数函数来模拟生成六位随机数经过处理一下后，前者作为验证码后者作为颜色的十六进制六位表示值。