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;
    }

<data>
    <instance id="attachmentDc"
              class="files.ex1.entity.Attachment">
        <fetchPlan extends="_base"/>
        <loader/>
    </instance>
</data>
<layout spacing="true">
    <form dataContainer="attachmentDc">
        <column>
            <fileStorageUpload id="fileField" property="file"/>

<groupTable id="attachmentsTable"
            width="100%"
            dataContainer="attachmentsDc">
    <columns>
        <column id="fileName" caption="File"/>

@Autowired
private UiComponents uiComponents;
@Autowired
private Downloader downloader; (1)

@Install(to = "attachmentsTable.fileName", subject = "columnGenerator")
private Component attachmentsTableFileColumnGenerator(Attachment attachment) {
    if (attachment.getFile() != null) {
        LinkButton linkButton = uiComponents.create(LinkButton.class);
        linkButton.setAction(new BaseAction("download")
                .withCaption(attachment.getFile().getFileName())
                .withHandler(actionPerformedEvent ->
                        downloader.download(attachment.getFile()) (2)
                )
        );
        return linkButton;
    } else {
        return new Table.PlainTextCell("<empty>");
    }
}

@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);
    }
}