简易验证码

生成，检验

效果：

示例

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;

@WebServlet("/captcha")
public class CaptchaServlet extends HttpServlet {

    // 处理生成验证码图片的请求
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 设置响应类型为图片
        response.setContentType("image/jpeg");

        // 设置验证码内容
        String captchaText = generateCaptchaText();

        // 将验证码存储到 session 中
        request.getSession().setAttribute("captcha", captchaText);

        // 创建验证码图片
        BufferedImage image = new BufferedImage(100, 40, BufferedImage.TYPE_INT_RGB);
        Graphics2D graphics = image.createGraphics();
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0, 0, 100, 40);
        graphics.setFont(new Font("Arial", Font.BOLD, 30));
        graphics.setColor(Color.BLACK);
        graphics.drawString(captchaText, 10, 30);

        // 输出验证码图片
        OutputStream out = response.getOutputStream();
        javax.imageio.ImageIO.write(image, "JPEG", out);
        out.close();
    }

    // 生成随机的验证码文本
    private String generateCaptchaText() {
        String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        StringBuilder captcha = new StringBuilder();
        Random random = new Random();
        for (int i = 0; i < 4; i++) {
            int index = random.nextInt(characters.length());
            captcha.append(characters.charAt(index));
        }
        return captcha.toString();
    }

    // 检查用户提交的验证码是否正确（忽略大小写）
    public static boolean validateCaptcha(HttpServletRequest request, String userInputCaptcha) {
        String sessionCaptcha = (String) request.getSession().getAttribute("captcha");
        if (sessionCaptcha == null) {
            return false; // 验证码已过期或不存在
        }
        return sessionCaptcha.equalsIgnoreCase(userInputCaptcha);
    }
}

请求地址

http://localhost:8080/captcha