java生成二维码及下载

以下是使用Java生成二维码并下载的方法：

1. 使用QRCode.jar包生成二维码：

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.imageio.ImageIO;
import com.google.zxing.BarcodeFormat;
import com.google.zxing.EncodeHintType;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;

public class QRCodeGenerator {
    public static void main(String[] args) {
        String qrCodeText = "https://www.example.com"; // 二维码内容
        String filePath = "path/to/save/qrcode.png"; // 保存二维码的文件路径
        int size = 250; // 二维码尺寸

        try {
            Map<EncodeHintType, Object> hints = new HashMap<>();
            hints.put(EncodeHintType.CHARACTER_SET, "UTF-8");

            QRCodeWriter qrCodeWriter = new QRCodeWriter();
            BitMatrix bitMatrix = qrCodeWriter.encode(qrCodeText, BarcodeFormat.QR_CODE, size, size, hints);

            BufferedImage bufferedImage = new BufferedImage(size, size, BufferedImage.TYPE_INT_RGB);
            for (int x = 0; x < size; x++) {
                for (int y = 0; y < size; y++) {
                    bufferedImage.setRGB(x, y, bitMatrix.get(x, y) ? 0x000000 : 0xFFFFFF);
                }
            }

            File qrCodeFile = new File(filePath);
            ImageIO.write(bufferedImage, "png", qrCodeFile);
            System.out.println("二维码生成成功！");

        } catch (WriterException | IOException e) {
            e.printStackTrace();
        }
    }
}

2. 下载生成的二维码：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;

public class QRCodeDownloader {
    public static void main(String[] args) {
        String filePath = "path/to/save/qrcode.png"; // 生成的二维码文件路径

        File qrCodeFile = new File(filePath);
        try (FileInputStream fis = new FileInputStream(qrCodeFile)) {
            HttpServletResponse response = null; // 获取HttpServletResponse对象

            response.setContentType("image/png");
            response.setHeader("Content-Disposition", "attachment; filename=\"qrcode.png\"");

            ServletOutputStream outputStream = response.getOutputStream();
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fis.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            outputStream.flush();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

请注意，以上代码仅为示例，需要根据实际情况进行适当修改。