Использование хранилища файлов

@JmixEntity
@Entity
@Table(name = "ATTACHMENT")
public class Attachment {
    // ...

    @Column(name = "FILE_")
    private FileRef file;

    public FileRef getFile() {
        return file;
    }

    public void setFile(FileRef file) {
        this.file = file;
    }

<iframe/>
<formLayout id="form" dataContainer="attachmentDc">
    <fileStorageUploadField id="fileField" property="file"/>

@ViewComponent
private DataGrid<Attachment> attachmentsDataGrid;

@Autowired
private UiComponents uiComponents;

@Autowired
private Downloader downloader; (1)

@Subscribe
public void onInit(final InitEvent event) {
    attachmentsDataGrid.addComponentColumn(attachment -> {
        Button button = uiComponents.create(Button.class);
        button.setText("Download");
        button.addThemeName("tertiary-inline");
        button.addClickListener(clickEvent -> {
            downloader.download(attachment.getFile()); (2)
        });
        return button;
    });
}

@Autowired
private FileStorageLocator fileStorageLocator; (1)
@Autowired
private DataManager dataManager;

private void getAndSaveImage() {
    try {
        (2)
        URLConnection connection = new URL("https://picsum.photos/300").openConnection();
        try (InputStream responseStream = connection.getInputStream()) {
            (3)
            FileStorage fileStorage = fileStorageLocator.getDefault();
            FileRef fileRef = fileStorage.saveStream("photo.jpg", responseStream);
            (4)
            Attachment attachment = dataManager.create(Attachment.class);
            attachment.setFile(fileRef);
            dataManager.save(attachment);
        }
    } catch (IOException e) {
        throw new RuntimeException("Error getting image", e);
    }
}

private void saveToLocalFile(Attachment attachment, Path path) {
    FileStorage fileStorage = fileStorageLocator.getDefault();
    FileRef fileRef = attachment.getFile();
    (5)
    InputStream inputStream = fileStorage.openStream(fileRef);
    try {
        (6)
        Files.copy(inputStream, path.resolve(fileRef.getFileName()),
                StandardCopyOption.REPLACE_EXISTING);
    } catch (IOException e) {
        throw new RuntimeException("Error saving image", e);
    }
}