java如何实现生成带颜色背景的4位验证码

生成带颜色背景的4位验证码可以通过 Java 的 Graphics2D 类和 Random 类实现。以下是一个简单的示例代码：

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.util.Random;

public class CaptchaGenerator {
    private static final int WIDTH = 80; // 验证码图片宽度
    private static final int HEIGHT = 30; // 验证码图片高度
    private static final int CODE_LENGTH = 4; // 验证码长度
    private static final String CODE_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"; // 验证码字符集

    public static BufferedImage generateCaptcha() {
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = (Graphics2D) image.getGraphics();
        Random random = new Random();

        // 生成随机颜色的背景
        g.setColor(new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256)));
        g.fillRect(0, 0, WIDTH, HEIGHT);

        // 生成验证码
        StringBuilder code = new StringBuilder();
        for (int i = 0; i < CODE_LENGTH; i++) {
            char c = CODE_CHARACTERS.charAt(random.nextInt(CODE_CHARACTERS.length()));
            code.append(c);
            g.setColor(new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256)));
            g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 20));
            g.drawString(String.valueOf(c), 15 + i * 15, 20);
        }

        // 添加干扰线
        for (int i = 0; i < 5; i++) {
            g.setColor(new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256)));
            int x1 = random.nextInt(WIDTH);
            int y1 = random.nextInt(HEIGHT);
            int x2 = random.nextInt(WIDTH);
            int y2 = random.nextInt(HEIGHT);
            g.drawLine(x1, y1, x2, y2);
        }

        g.dispose();
        return image;
    }
}

调用 `generateCaptcha()` 方法即可生成一个带颜色背景的 4 位验证码的 BufferedImage 对象。你可以通过将其保存到文件或输出到流中来使用它。