java - java中如何保存图像文件？

Question

我正在用java开发一个QR生成器应用程序。这是生成代码，

try {

            ByteArrayOutputStream out = QRCode.from(txt_input.getText()).to(ImageType.PNG).stream();
            ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());

            BufferedImage image = ImageIO.read(in);

            lbl_output.setIcon(null);
            lbl_output.setIcon(new ImageIcon(image));

            String pic = "image";

        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, " Please enter valid text !");
        }

生成QR图像后，我需要保存它。所以我使用了这段代码，

JFileChooser save = new JFileChooser();
int response = save.showSaveDialog(null);

            if (response == JFileChooser.APPROVE_OPTION) {
               try {
                    File fileToSave = new File(pic + ".png");
                    ImageIO.write(image, "PNG", fileToSave);

                } catch (Exception e) {

                }
             }

但是有一个异常(exception)，例如，

java.lang.IllegalArgumentException: image == null!
    at javax.imageio.ImageTypeSpecifier.createFromRenderedImage(ImageTypeSpecifier.java:925)
    at javax.imageio.ImageIO.getWriter(ImageIO.java:1591)
    at javax.imageio.ImageIO.write(ImageIO.java:1520)

Answer 1

这里没有理由使用ImageIO，因为您的QRCode类已经将PNG格式的图像写入字节数组。

相反，只需将字节复制到您想要的文件即可。

即:

ByteArrayOutputStream out = QRCode.from(txt_input.getText()).to(ImageType.PNG).stream();
byte[] bytes = out.toByteArray();

...

FileChooser save = new JFileChooser();
int response = save.showSaveDialog(null);

if (response == JFileChooser.APPROVE_OPTION) {
    File fileToSave = new File(pic + ".png");

    // Try-with-resource
    try (OutputStream out = new FileOutputStream(fileToSave)) {
        out.write(bytes);
        out.flush();
    }
}