如何在Java中添加动态验证码

I want to add dynamic captcha on page.Whenever more than 3 request comes inspecific time from same IP address then Captcha will appear on the screen..

我想在页面上添加动态验证码。每当有超过3个请求来自同一IP地址的特定时间时，屏幕上会出现Captcha ..

3 个解决方案

#1

You can write a code in servlet filter to check if many requests come from a specific IP within a specific time duration. In this case, you can add some flag in the session.

您可以在servlet过滤器中编写代码，以检查在特定持续时间内是否有来自特定IP的许多请求。在这种情况下，您可以在会话中添加一些标志。
Use this flag to check on the page if to display the captcha or not.

使用此标志检查页面是否显示验证码。

#2

Create a servlet which dynamically creates the captcha. To create the captcha you can use ImageMagick in conjunction with im4java.
创建一个动态创建验证码的servlet。要创建验证码，您可以将ImageMagick与im4java结合使用。
In your HTML page embed an Image-Tag with the path to the servlet which generates the captcha.
在HTML页面中嵌入一个Image-Tag，其中包含生成验证码的servlet的路径。
Count the number of requests to the captcha-generating servlet in your session. As long as the threshold has not been reached you may return an empty image to avoid any errors on the client side.
计算会话中生成验证码的servlet的请求数。只要未达到阈值，您可以返回空图像以避免客户端出现任何错误。
If the threshold has been reached you generate the captcha. Store the value (i.e. the value the user has to enter in order to proceed) in the session.
如果已达到阈值，则生成验证码。在会话中存储值（即用户必须输入的值才能继续）。
The user sees the captcha and has to enter its value.
用户看到验证码并且必须输入其值。
Compare the value the user has entered with the value stored in the session.
将用户输入的值与会话中存储的值进行比较。

I hope this helps.

我希望这有帮助。

#3

-1

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a test to determine whether the user is human or not.

CAPTCHA（完全自动公共图灵测试告诉计算机和人类除外）是一项测试，以确定用户是否是人。

CAPTCHA provides a way to block bots from interacting with your site by providing something that's hard for them to read, but easy for people to read.

CAPTCHA提供了一种方法，通过提供难以阅读的内容来阻止机器人与您的网站进行交互，但人们可以轻松阅读。

import java.util.Random;
public class GenerateCaptcha {
      /**
       * Generate Length between 5 and 8.
       * @return return length.
       */
      private static int generateRandomLength() {
            int length = 5 + Math.abs((random.nextInt()%4));
            return length;
      }

      /**
       *  Generate a CAPTCHA String consisting of random
       *  lower case & upper case letters, and numbers.
       */
      private static String generateCaptchaString(int length) {

            StringBuffer captchaBuffer = new StringBuffer();

            for (int i = 0; i < length; i++) {

                  /** Generate the Random Character between 0 to 61.
                   * NOTE: Take abs value, because there may
                   * be ArrayIndexOutOfBount
                   * Exception for negative number*/
                  int rndCharIdx = Math.abs(random.nextInt()) % 62;

                  char character = characters[rndCharIdx];

                  captchaBuffer.append(character);
            }
            return captchaBuffer.toString();
      }

      private static Character[] characters = {'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','0','1','2','3','4','5','6','7','8','9'};

      private static Random random = new Random();

      public static void main(String[] args) {

            int rndmCaptchaLen = generateRandomLength();

            String captcha = generateCaptchaString(rndmCaptchaLen);

            System.out.println("Random Captcha #"+captcha);
      }
}

More information on my blog:

#1

You can write a code in servlet filter to check if many requests come from a specific IP within a specific time duration. In this case, you can add some flag in the session.

您可以在servlet过滤器中编写代码，以检查在特定持续时间内是否有来自特定IP的许多请求。在这种情况下，您可以在会话中添加一些标志。
Use this flag to check on the page if to display the captcha or not.

使用此标志检查页面是否显示验证码。

#2

Create a servlet which dynamically creates the captcha. To create the captcha you can use ImageMagick in conjunction with im4java.
创建一个动态创建验证码的servlet。要创建验证码，您可以将ImageMagick与im4java结合使用。
In your HTML page embed an Image-Tag with the path to the servlet which generates the captcha.
在HTML页面中嵌入一个Image-Tag，其中包含生成验证码的servlet的路径。
Count the number of requests to the captcha-generating servlet in your session. As long as the threshold has not been reached you may return an empty image to avoid any errors on the client side.
计算会话中生成验证码的servlet的请求数。只要未达到阈值，您可以返回空图像以避免客户端出现任何错误。
If the threshold has been reached you generate the captcha. Store the value (i.e. the value the user has to enter in order to proceed) in the session.
如果已达到阈值，则生成验证码。在会话中存储值（即用户必须输入的值才能继续）。
The user sees the captcha and has to enter its value.
用户看到验证码并且必须输入其值。
Compare the value the user has entered with the value stored in the session.
将用户输入的值与会话中存储的值进行比较。