javaweb生成验证码图片的代码

以下是一个简单的 JavaWeb 生成验证码图片的代码示例：

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class VerifyCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final int WIDTH = 80; // 验证码图片的宽度
    private static final int HEIGHT = 30; // 验证码图片的高度
    private static final int CODE_COUNT = 4; // 验证码字符数
    private static final int LINE_COUNT = 20; // 干扰线数

    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        // 设置响应头信息，禁止缓存
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "No-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("image/jpeg");

        // 创建图片缓存区
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();

        // 设置背景色并绘制矩形框
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, WIDTH, HEIGHT);
        g.setColor(Color.GRAY);
        g.drawRect(0, 0, WIDTH - 1, HEIGHT - 1);

        // 生成随机数并将其转换为字符串
        Random random = new Random();
        String code = "";
        for (int i = 0; i < CODE_COUNT; i++) {
            int c = random.nextInt(10);
            code += c;
        }

        // 将生成的验证码存入 session 中
        HttpSession session = request.getSession();
        session.setAttribute("verifyCode", code);

        // 绘制干扰线
        for (int i = 0; i < LINE_COUNT; i++) {
            int x1 = random.nextInt(WIDTH);
            int y1 = random.nextInt(HEIGHT);
            int x2 = random.nextInt(WIDTH);
            int y2 = random.nextInt(HEIGHT);
            g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
            g.drawLine(x1, y1, x2, y2);
        }

        // 绘制验证码
        Font font = new Font("Arial", Font.BOLD, 20);
        g.setFont(font);
        for (int i = 0; i < CODE_COUNT; i++) {
            g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
            g.drawString(String.valueOf(code.charAt(i)), 20 * i + 6, 25);
        }

        // 输出图片
        try {
            ServletOutputStream out = response.getOutputStream();
            ImageIO.write(image, "JPEG", out);
            out.flush();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        doGet(request, response);
    }
}

在 `doGet` 方法中，首先设置响应头信息，禁止缓存，然后创建一个 `BufferedImage` 对象用来存储验证码图片。接着设置背景色并绘制矩形框，生成随机数并将其转换为字符串，将生成的验证码存入 session 中，然后绘制干扰线和验证码。最后将生成的图片通过 `ServletOutputStream` 输出到浏览器中。在 `doPost` 方法中，直接调用 `doGet` 方法。