Upload

Upload is a component for uploading one or more files. It shows the upload progression and status of each file. Files can be uploaded using the Upload button or via drag and drop.

Open in a
new tab
MultiFileMemoryBuffer buffer = new MultiFileMemoryBuffer();
Upload upload = new Upload(buffer);

upload.addSucceededListener(event -> {
    String fileName = event.getFileName();
    InputStream inputStream = buffer.getInputStream(fileName);

    // Do something with the file data
    // processFile(inputStream, fileName);
});

Handling Uploaded Files

The Java Flow Upload component provides an API to handle uploaded file data directly, without having to set up an endpoint or a servlet. It uses a Receiver implementation to write the incoming file data into an OutputStream.

The following default implementations of Receiver are available:

MemoryBuffer

Handles a single file upload at once, writes the file data into an in-memory buffer. Using MemoryBuffer automatically configures the component so that only a single file can be selected.

MultiFileMemoryBuffer

Handles multiple file uploads at once, writes the file data into a set of in-memory buffers.

FileBuffer

Handles a single file upload at once, saves a file on the system. Files are going to be saved into the current working directory of the Java application. Using FileBuffer automatically configures the component so that only a single file can be selected.

MultiFileMemoryBuffer

Handles multiple file uploads at once, and for each, saves a file on the system. Files are going to be saved into the current working directory of the Java application.

/* Example for MemoryBuffer */
MemoryBuffer memoryBuffer = new MemoryBuffer();
Upload singleFileUpload = new Upload(memoryBuffer);

singleFileUpload.addSucceededListener(event -> {
    // Get information about the uploaded file
    InputStream fileData = memoryBuffer.getInputStream();
    String fileName = event.getFileName();
    long contentLength = event.getContentLength();
    String mimeType = event.getMIMEType();

    // Do something with the file data
    // processFile(fileData, fileName, contentLength, mimeType);
});

/* Example for MultiFileMemoryBuffer */
MultiFileMemoryBuffer multiFileMemoryBuffer = new MultiFileMemoryBuffer();
Upload multiFileUpload = new Upload(multiFileMemoryBuffer);

multiFileUpload.addSucceededListener(event -> {
    // Determine which file was uploaded
    String fileName = event.getFileName();

    // Get input stream specifically for the finished file
    InputStream fileData = multiFileMemoryBuffer.getInputStream(fileName);
    long contentLength = event.getContentLength();
    String mimeType = event.getMIMEType();

    // Do something with the file data
    // processFile(fileData, fileName, contentLength, mimeType);
});

For more advanced use-cases, you can provide custom implementations for Receiver or MultiFileReceiver, for example to save files into a specific directory, or uploading them to a Cloud storage.

Drag & Drop

Upload supports drag and drop for uploading files. Multiple files can be dropped simultaneously. By default, it’s enabled on desktop and disabled on touch devices. By explicitly setting it to enabled or disabled affects both desktop and mobile devices.

Open in a
new tab
Upload dropEnabledUpload = new Upload(buffer1);
dropEnabledUpload.setDropAllowed(true);

Upload dropDisabledUpload = new Upload(buffer2);
dropDisabledUpload.setDropAllowed(false);

Auto Upload

By default, files are uploaded immediately as they are added to the queue. Auto upload can be disabled, for example, to allow the user to review the list of files before initiating their upload by clicking the ▶️ button for each file. It is recommended to change the button label to indicate that uploads do not start automatically.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setAutoUpload(false);

UploadExamplesI18N i18n = new UploadExamplesI18N();
i18n.getAddFiles()
        .setMany("Select Files...");
upload.setI18n(i18n);

Uploads can be initiated programmatically when auto upload is disabled, for example if you want to provide the user with a single button to start all uploads.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setAutoUpload(false);

Button uploadAllButton = new Button("Upload All Files");
uploadAllButton.addThemeVariants(ButtonVariant.LUMO_PRIMARY);
uploadAllButton.addClickListener(event -> {
    // No explicit Flow API for this at the moment
    upload.getElement().callJsFunction("uploadFiles");
});

Upload Restrictions

You can set three types of restrictions: file format, file count and file size.

Exceptions that arise from the user violating any of the imposed restrictions aren’t shown in the UI by default. Use a File Rejected listener to catch these exceptions and, for example, a Notification to inform the user about the problem at hand and any potential solutions.

However, the user should be informed upfront about any file upload restrictions. Maximum number of files allowed, file size and format limitations should all be communicated clearly to avoid exceptions whenever possible.

File Format

Upload can be configured to only accept files of specific formats. The acceptable file formats are set using MIME type patterns or file extensions, for example "video/*", "image/tiff" or ".pdf" and "audio/mp3".

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setAcceptedFileTypes("application/pdf", ".pdf");

upload.addFileRejectedListener(event -> {
    String errorMessage = event.getErrorMessage();

    Notification notification = Notification.show(
            errorMessage,
            5000,
            Notification.Position.MIDDLE
    );
    notification.addThemeVariants(NotificationVariant.LUMO_ERROR);
});
Note
Prefer MIME-type

While MIME types are widely supported, file extensions are only implemented in certain browsers and should be avoided.

File Count

Upload does not limit the number of files that can be uploaded by default. If you set the maximum to one the native file browser prevents selecting multiple files.

Note
Receiver-specific Restrictions

When using a Receiver that does not implement the MultiFileReceiver interface, such as MemoryBuffer or FileBuffer, the Upload component will automatically limit the number of files to one. That is because these receiver implementations only support handling a single file at once.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setMaxFiles(3);

upload.addFileRejectedListener(event -> {
    String errorMessage = event.getErrorMessage();

    Notification notification = Notification.show(
            errorMessage,
            5000,
            Notification.Position.MIDDLE
    );
    notification.addThemeVariants(NotificationVariant.LUMO_ERROR);
});

File Size

Upload allows you to limit the file size by setting a maximum. The limit is defined in bytes. It’s unlimited by default.

Open in a
new tab
Upload upload = new Upload(buffer);

int maxFileSizeInBytes = 10 * 1024 * 1024; // 10MB
upload.setMaxFileSize(maxFileSizeInBytes);

upload.addFileRejectedListener(event -> {
    String errorMessage = event.getErrorMessage();

    Notification notification = Notification.show(
            errorMessage,
            5000,
            Notification.Position.MIDDLE
    );
    notification.addThemeVariants(NotificationVariant.LUMO_ERROR);
});
Note
Revalidate the size limit in the server

This constraint is set on the client and is checked before contacting the server.

File Actions

Each file has a certain set of associated actions available depending on its upload state. A file always has a "Clear/Remove" button. This button cancels the upload (if applicable) and removes the file from the list.

The "Clear/Remove" button is the only available action during and after a successful upload.

Open in a
new tab
import { html, LitElement, customElement } from 'lit-element';
import '@vaadin/vaadin-upload/vaadin-upload';
import { applyTheme } from 'Frontend/generated/theme';

function createFakeFiles() {
  return createFakeUploadFiles([
    {
      name: 'Workflow.pdf',
      progress: 60,
      status: '19.7 MB: 60% (remaining time: 00:12:34)',
    },
    { name: 'Financials.xlsx', complete: true },
  ]);
}

@customElement('upload-clear-button')
export class Example extends LitElement {
  protected createRenderRoot() {
    const root = super.createRenderRoot();
    // Apply custom theme (only supported if your app uses one)
    applyTheme(root);
    return root;
  }

  render() {
    return html`<vaadin-upload .files="${createFakeFiles()}"></vaadin-upload>`;
  }
}
Note
Remember to remove the file from the back end

The "Clear/Remove" button does not remove a successfully uploaded file from the server file system or database. It is only removed from Upload’s file list.

If an error or exception occurs Upload displays a "Retry" button that attempts to upload the file again when pressed.

Open in a
new tab
import { html, LitElement, customElement } from 'lit-element';
import '@vaadin/vaadin-upload/vaadin-upload';
import { applyTheme } from 'Frontend/generated/theme';

function createFakeFiles() {
  return createFakeUploadFiles([
    { name: 'Financials.xlsx', error: 'Something went wrong, please try again' },
  ]);
}

@customElement('upload-retry-button')
export class Example extends LitElement {
  protected createRenderRoot() {
    const root = super.createRenderRoot();
    // Apply custom theme (only supported if your app uses one)
    applyTheme(root);
    return root;
  }

  render() {
    return html`<vaadin-upload .files="${createFakeFiles()}"></vaadin-upload>`;
  }
}

When a file is queued (auto upload disabled) it has a "Start" Button that the user must press to begin the upload process.

Open in a
new tab
import { html, LitElement, customElement } from 'lit-element';
import '@vaadin/vaadin-upload/vaadin-upload';
import { applyTheme } from 'Frontend/generated/theme';

function createFakeFiles() {
  return createFakeUploadFiles([
    {
      name: 'Workflow.pdf',
      status: 'Queued',
      held: true,
    },
  ]);
}

@customElement('upload-start-button')
export class Example extends LitElement {
  protected createRenderRoot() {
    const root = super.createRenderRoot();
    // Apply custom theme (only supported if your app uses one)
    applyTheme(root);
    return root;
  }

  render() {
    return html`<vaadin-upload .files="${createFakeFiles()}"></vaadin-upload>`;
  }
}

Internationalization (i18n)

All of Upload’s labels and messages are configurable. For a complete list please refer to the API documentation (Java).

Open in a
new tab
Upload upload = new Upload(buffer);

// Please see the separate UploadFinnishI18N class / file
// in this example for the I18N configuration
UploadFinnishI18N i18N = new UploadFinnishI18N();
upload.setI18n(i18N);

Customization

You can replace the default upload button. For example, if Upload needs a stronger emphasis you can use a primary button.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setAcceptedFileTypes("application/pdf", ".pdf");

Button uploadButton = new Button("Upload PDF...");
uploadButton.addThemeVariants(ButtonVariant.LUMO_PRIMARY);

upload.setUploadButton(uploadButton);

// Disable the upload button after the file is selected
// Re-enable the upload button after the file is cleared
upload.getElement().addEventListener("max-files-reached-changed", event -> {
    boolean maxFilesReached = event.getEventData().getBoolean("event.detail.value");
    uploadButton.setEnabled(!maxFilesReached);
}).addEventData("event.detail.value");

You can also customize the drop label, as well as the icon.

Open in a
new tab
Upload upload = new Upload(buffer);

Span dropLabel = createDropLabel();
Icon dropIcon = VaadinIcon.CLOUD_UPLOAD_O.create();

upload.setDropLabel(dropLabel);
upload.setDropLabelIcon(dropIcon);
Note
Use a large drop target

When customizing the Upload component make sure not to make the drop target too small. A large drop target is easier to use and less error prone.

Technical

Listeners

Upload has listeners for the following events:

EventDescription

All Finished

Triggered when Upload has processed all the files in its queue, regardless of whether all the uploads were successful or not

Failed

When the upload is received but the reception is interrupted for some reason

File Rejected

Sent when the file selected for upload doesn’t meet the constraints, for example, file size

Finished

Sent when Upload receives a file regardless of whether the upload was successful or not (to distinguish between the two cases use either Succeeded or Failed listeners)

Progress

Event for tracking upload progress

Started

Triggered when the upload starts

Succeeded

Sent when the upload has been successfully received

Best Practices

Labelling

Choose labels that are informative and instructional. For example, if the user is to upload a single PDF file, it’s better to have the button label say "Upload PDF…​" instead of "Upload File…". The task becomes clearer and improves accessibility for the user, especially if they’re using a screen reader as the button’s label is read aloud when focused.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setAcceptedFileTypes("application/pdf", ".pdf");

UploadExamplesI18N i18n = new UploadExamplesI18N();
i18n.getAddFiles().setOne("Upload PDF...");
i18n.getDropFiles().setOne("Drop PDF here");
i18n.getError()
        .setIncorrectFileType(
                "The provided file does not have the correct format. Please provide a PDF document.");
upload.setI18n(i18n);

Likewise, if the user is expected to upload a spreadsheet but multiple file formats are accepted, have the button say "Upload Spreadsheet" with helpers to inform the user which formats are accepted.

Open in a
new tab
H4 title = new H4("Upload spreadsheet");
Paragraph hint = new Paragraph(
        "File size must be less than or equal to 1 MB. Only Excel and CSV files are accepted.");

Upload upload = new Upload(buffer);
upload.setAcceptedFileTypes(
        // Microsoft Excel (.xls)
        "application/vnd.ms-excel",
        ".xls",
        // Microsoft Excel (OpenXML, .xlsx)
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
        ".xlsx",
        // Comma-separated values (.csv)
        "text/csv",
        ".csv"
);

UploadExamplesI18N i18n = new UploadExamplesI18N();
i18n.getAddFiles().setOne("Upload Spreadsheet...");
i18n.getDropFiles().setOne("Drop spreadsheet here");
i18n.getError()
        .setIncorrectFileType(
                "Please provide the file in one of the supported formats (.xls, .xlsx, .csv).");
upload.setI18n(i18n);

add(title, hint, upload);

Error Messages

Try to provide meaningful feedback and error messages when an exception or error occurs. Avoid technical jargon and instead try to provide solutions/instructions on how to fix the error.

A "Server Unavailable" might suffice for tech savvy users but for some it might not be helpful at all. Your error messages should be written with your users in mind.

Open in a
new tab
Upload upload = new Upload(buffer);
upload.setDropAllowed(false);

UploadExamplesI18N i18N = new UploadExamplesI18N();
i18N.getUploading()
        .getError()
        .setUnexpectedServerError(
                "File couldn't be uploaded, please try again later");
upload.setI18n(i18N);

Progress Bar

Component for showing task completion progress.