java - 使用 Vaadin 和 Java 缩放图像

Question

我有以下代码来上传图片并在网页上显示

// Show uploaded file in this placeholder
final Embedded image = new Embedded("Uploaded Image");
image.setVisible(false);

// Implement both receiver that saves upload in a file and
// listener for successful upload
class ImageUploader implements Receiver, SucceededListener {
    public File file;

    public OutputStream receiveUpload(String filename, String mimeType) {
        // Create upload stream
        FileOutputStream fos = null; // Stream to write to
        try {
            // Open the file for writing.
            file = new File(tmp_dir + "/" + filename);
            fos = new FileOutputStream(file);
        } catch (final java.io.FileNotFoundException e) {                  
            return null;
        }
        return fos; // Return the output stream to write to
    }

    public void uploadSucceeded(SucceededEvent event) {     
        // Show the uploaded file in the image viewer
        image.setVisible(true);             
        image.setSource(new FileResource(file));                
    }
};
ImageUploader receiver = new ImageUploader(); 

// Create the upload with a caption and set receiver later
Upload upload = new Upload("Upload Image Here", receiver);
upload.setButtonCaption("Start Upload");
upload.addSucceededListener(receiver);  

final FormLayout fl = new FormLayout();
fl.setSizeUndefined();
fl.addComponents(upload, image);

问题是，它显示了完整的分辨率，我想将它缩放(以便它保持比例)到 180 像素宽度。图片还需要另存为原始文件名_resized.jpg，但我似乎无法按比例缩放。网络上的一些指南讨论了调整大小(但随后图片变形)或者它给 Vaadin 带来了一些问题。

更新: 添加了 scarl jar(来自 this answer))，因为使用以下代码会很容易:

BufferedImage scaledImage = Scalr.resize(image, 200);

但这会产生以下错误:

The method resize(BufferedImage, int, BufferedImageOp...) in the type Scalr is not applicable for the arguments (Embedded, int)

而且我无法转换，因为 Cannot cast from Embedded to BufferedImage 错误

更新:使用以下代码我可以转换为正确的类型

File imageFile = (((FileResource) (image.getSource())).getSourceFile());
BufferedImage originalImage = ImageIO.read(imageFile) ;

BufferedImage scaledImage = Scalr.resize(originalImage, 200);

但现在我无法显示图像..

final FormLayout fl = new FormLayout();
fl.setSizeUndefined();       
fl.addComponents(upload, scaledImage);

由于错误 AbstractComponentContainer 类型中的方法 addComponents(Component...) 不适用于参数 (Upload, BufferedImage)

Answer 1

您不能直接将 Vaadin 对象与第三方工具(例如 Scalr)一起使用，而无需将一个对象适配到另一个。 “Embedded”是一个 Vaadin 类，而 SclaR 需要一个“BufferedImage”。

因此，您首先需要从 Embedded 对象中提取 File 对象:

File imageFile = ((FileResource)(image.getSource()).getSourceFile();

然后，使用 ImageIO 将其加载到 BufferedImage 中，如您指向的链接中所述 (What is the best way to scale images in Java?)

BufferedImage img = ImageIO.read(...); // load image

然后，您就有了要查找的 BufferedImage 对象。