用ZXing生成二维码后使用Thumbnailator添加水印，水印变成黑白，该如何解决？

你可以先生成二维码，然后将它转换为高位深度的 BufferedImage，最后使用 Thumbnailator 添加水印就可以了:

import com.google.zxing.*;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;
import net.coobird.thumbnailator.Thumbnails;
import net.coobird.thumbnailator.geometry.Positions;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class QRCodeWatermarkExample {
    public static void main(String[] args) throws WriterException, IOException {
        // 生成二维码
        QRCodeWriter qrCodeWriter = new QRCodeWriter();
        BitMatrix bitMatrix = qrCodeWriter.encode("https://example.com", BarcodeFormat.QR_CODE, 300, 300);

        BufferedImage qrCodeImage = toBufferedImage(bitMatrix);

        // 将二维码转换为高位深度的 BufferedImage
        BufferedImage convertedImage = new BufferedImage(qrCodeImage.getWidth(), qrCodeImage.getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = convertedImage.createGraphics();
        g2d.drawImage(qrCodeImage, 0, 0, null);
        g2d.dispose();

        // 读取水印图片
        BufferedImage watermarkImage = ImageIO.read(new File("path/to/watermark/image.png"));

        // 使用 Thumbnailator 添加水印
        BufferedImage watermarkedImage = Thumbnails.of(convertedImage)
                .size(300, 300)
                .watermark(Positions.BOTTOM_RIGHT, watermarkImage, 0.5f)
                .asBufferedImage();

        // 保存最终图像
        ImageIO.write(watermarkedImage, "png", new File("output.png"));
    }

    private static BufferedImage toBufferedImage(BitMatrix matrix) {
        int width = matrix.getWidth();
        int height = matrix.getHeight();
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_BINARY);

        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                image.setRGB(x, y, matrix.get(x, y) ? Color.BLACK.getRGB() : Color.WHITE.getRGB());
            }
        }
        return image;
    }
}