从image对象获取图像mime类型

Question

我有一个桌面java应用程序，它从用户剪贴板获取图像(“粘贴”操作)，我需要在进一步处理之前检查它们的mime类型(只允许jpg，png和gif )。

我使用以下代码从剪贴板获取图像：

  Transferable transferable = Toolkit.getDefaultToolkit().getSystemClipboard().getContents(null);
  if (transferable != null && transferable.isDataFlavorSupported(DataFlavor.imageFlavor)) {
    try {
      Image pastedImage = (Image) transferable.getTransferData(DataFlavor.imageFlavor);
      // how to get mime type?
    } catch (Exception e) {/*cutted for brevity*/}
  }

现在，我知道how to get the mime type from a file using apache Tika和我已经尝试过将图像写入磁盘以重用此技术，但ImageIO.write方法还需要一个格式名称：

BufferedImage bi = convertImageToBI(img);
File outputfile = File.createTempFile("img_", "_upload");
ImageIO.write(bi, "jpg", outputfile);

为了将图像转换为BufferedImage，我使用了this method。唯一的区别是我使用的是TYPE_INT_RGB而不是TYPE_INT_ARGB。

如何获取粘贴图像的mime类型？

Answer 1

我尝试了一种疯狂的方法来检查它是JPG/GIF还是PNG。当有透明度时，我使用PNG，除此之外我总是使用JPG，这也被证明可以与GIF一起工作，只是GIF失去了它的动画效果

    protected BufferedImage img;

    protected void loadImage() {
        try {
            // Well we read the temp file first, I test it using local file
            File f = new File(loc);
            // Read the file as Image 
            this.img = ImageIO.read(f);
        } catch(Exception e) {
            JOptionPane.showMessageDialog(this, e.getMessage());
        }
        this.revalidate();
        this.repaint();
    }

    public byte[] toBlob() {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            // Check if this image contains transparency? If no then write as JPG
            if (this.img.getTransparency() == java.awt.Transparency.OPAQUE) {
                ImageIO.write((BufferedImage)this.img, "jpg", baos);
            } else { // If it does contain transparency then write as PNG
                ImageIO.write((BufferedImage)this.img, "png", baos);
            }
        } catch(Exception e) {
            JOptionPane.showMessageDialog(this, e.toString());
        }
        byte[] data = baos.toByteArray();
        return data;
    }
    
    public void saveImageToBlob(String location) {
        try {
            File f = new File(location);
            FileOutputStream o = new FileOutputStream(f);
            byte[] d = this.toBlob();
            o.write(d, 0, d.length);
            o.close();
        } catch(Exception e) {
            JOptionPane.showMessageDialog(this, e.toString());
        }
    }