Java生成二维码

要在Java中生成二维码，可以使用ZXing库。下面是一段示例代码，可以将一个字符串生成为二维码图片：

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
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;
import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel;

public class QRCodeWriter {
    public static void main(String[] args) {
        try {
            String text = "Hello, world!";
            int width = 200;
            int height = 200;
            String format = "png";
            String filePath = "qrcode.png";

            // set QR code parameters
            QRCodeWriter qrCodeWriter = new QRCodeWriter();
            BitMatrix bitMatrix = qrCodeWriter.encode(text, BarcodeFormat.QR_CODE, width, height);

            // create the BufferedImage object
            BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            image.createGraphics();

            // set white background
            Graphics2D graphics = (Graphics2D) image.getGraphics();
            graphics.setColor(Color.WHITE);
            graphics.fillRect(0, 0, width, height);

            // set QR code colors
            graphics.setColor(Color.BLACK);
            for (int i = 0; i < width; i++) {
                for (int j = 0; j < height; j++) {
                    if (bitMatrix.get(i, j)) {
                        graphics.fillRect(i, j, 1, 1);
                    }
                }
            }

            // save QR code image to file
            File qrCodeImage = new File(filePath);
            ImageIO.write(image, format, qrCodeImage);

            System.out.println("QR Code generation completed!");
        } catch (WriterException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

这段代码会将字符串"Hello, world!"生成为一个200x200像素的二维码图片，并保存到文件"qrcode.png"中。注意需要导入ZXing库及其依赖。