如何在 Vaadin 中使用 ByteArrayOutputStream 上传图像? [英] How to upload an image using ByteArrayOutputStream in Vaadin?

问题描述

我想以字节数组的形式接收上传的图像(以便它可以插入到 sql 数据库中).我还想将上传的图片显示为预览.

I want to receive an uploaded image as a byte array (so that it can be inserted into a sql database). I also want to show the uploaded image as a preview.

我尝试了以下代码，但我没有收到完整图像的字节.(如果我打印字节数组，它只打印几个字符)

I have tried the following code but im not receiving the bytes of the full image. (if i print the byte array it prints only a few characters)

final Embedded preview = new Embedded("Uploaded Image");
preview.setVisible(false);

final Upload upload = new Upload();
upload.setCaption("Image");

// Create upload stream
final ByteArrayOutputStream baos = new ByteArrayOutputStream(); // Stream to write to

upload.setReceiver(new Upload.Receiver() {
    @Override
    public OutputStream receiveUpload(String filename, String mimeType) {

        return baos; // Return the output stream to write to
    }
});

upload.addSucceededListener(new Upload.SucceededListener() {
    @Override
    public void uploadSucceeded(Upload.SucceededEvent succeededEvent) {
        final byte[] bytes = baos.toByteArray();

        preview.setVisible(true);
        preview.setSource(new StreamResource(new StreamResource.StreamSource() {
            @Override
            public InputStream getStream() {
                return new ByteArrayInputStream(bytes);
            }
        }, ""));

    }
});

推荐答案

您可以尝试将带有一些日志的 ProgressListener 添加到 Upload 以查看发生了什么；您将获得读取字节数和总内容长度作为 updateProgress 方法的参数，以便您可以查看是否正在发送所有内容.

You could try adding a ProgressListener with some logs to the Upload to see what is happening; you will get the amount of read bytes and total content length as a parameter to the updateProgress method so you can see if everything is being sent.

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