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Upload

Upload allows the user to upload files, giving feedback to the user during the upload process.

Usage
Styling

Handling Upload Requests (Client-Side Only)
Drag & Drop
Auto-Upload
Upload Restrictions
File Actions
Internationalization (i18n)
Customization
Technical
Best Practices
Related Components

Upload allows the user to upload files, giving feedback to the user during the upload process. It shows the upload progress and the status of each file. Files can be uploaded by clicking on the Upload button or by dragging them onto the component.

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{/* Use the target attribute to specify the URL that handles the file upload */}
<Upload
  target="/api/fileupload"
  files={createFakeFilesUploadBasic()}
  // ... other properties
/>

Handling Upload Requests (Client-Side Only)

When using the Upload web component standalone, you need to set up an upload file handler or endpoint in your backend to handle the file upload request. By default, the Upload component sends a request with the method type POST, the content type multipart/form-data, and the request URL (i.e., the current browser location).

Use the target attribute to specify a different URL that should handle the upload request. It’s also possible to customize other aspects of the request, such as the method or request headers.

Note	Web Component Only This section is only relevant when using the Upload web component standalone. The Java/Flow component has its own set of APIs to handle file data, directly. It doesn’t require the request to be handled manually.

<Upload
  method="PUT"
  target="/api/upload-handler"
  headers='{ "X-API-KEY": "7f4306cb-bb25-4064-9475-1254c4eff6e5" }'>
</Upload>

Drag & Drop

Upload allows the user to drag files onto the component to upload them. Multiple files can be dropped simultaneously. By default, this is enabled on desktop computers and disabled on touch devices. Explicitly setting it to enabled or disabled, though, affects both desktop and mobile devices.

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<Upload id="upload-drop-disabled" nodrop />

Auto-Upload

By default, files are uploaded immediately, or at least they’re 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’s recommended that you change the button label to communicate that uploads don’t start automatically.

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<Upload noAuto ref={uploadRef} files={createFakeFilesUploadAutoUploadDisabled()} />

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

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<Upload noAuto ref={uploadRef} files={createFakeFilesUploadAllFiles()} />

<Button theme="primary" onClick={() => uploadRef.current?.uploadFiles()}>
  Upload All Files
</Button>

Upload Restrictions

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

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

The user should be informed upfront, though, about any file upload restrictions. Limitations on the maximum number of files allowed, file size, and format should all be communicated clearly, to reduce or eliminate exceptions.

File Format

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

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<h4>Upload report</h4>
<p>Accepted file formats: PDF (.pdf)</p>
<Upload
  accept="application/pdf,.pdf"
  maxFiles={1}
  onFileReject={(event) => {
    Notification.show(event.detail.error);
  }}
/>

Note	Prefer MIME Type Although MIME types are widely supported, file extensions are only implemented in certain browsers and should be avoided.

File Count

By default, Upload doesn’t limit the number of files that can be uploaded. However, you can set a file count limit. If you set the maximum to one, the native file browser prevents multiple files from being selected.

Note

Java Flow-Specific

When using a Receiver that doesn’t implement the MultiFileReceiver interface — such as MemoryBuffer or FileBuffer — the Upload component automatically limits the number of files to one. This is because these receiver implementations only support handling a single file at once.

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const maxFiles = 3;

return (
  <>
    <h4>Upload files</h4>
    <p>Maximum of {maxFiles} files allowed</p>
    <Upload
      maxFiles={maxFiles}
      onFileReject={(event) => {
        Notification.show(event.detail.error);
      }}
    />
  </>
);

File Size

Upload allows you to limit the file size by setting a maximum amount in bytes. By default, though, there is no limit.

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const maxFileSizeInMB = 10;
const maxFileSizeInBytes = maxFileSizeInMB * 1024 * 1024;

return (
  <>
    <h4>Upload file</h4>
    <p>Maximum file size: {maxFileSizeInMB} MB</p>
    <Upload
      maxFiles={1}
      maxFileSize={maxFileSizeInBytes}
      onFileReject={(event) => {
        Notification.show(event.detail.error);
      }}
    />
  </>
);

Note	Revalidate Size Limit on 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.

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import React from 'react';
import { Upload } from '@hilla/react-components/Upload.js';
import { createFakeUploadFiles } from './upload-demo-helpers';

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

function Example() {
  return <Upload files={createFakeFiles()}></Upload>;
}

Note	Remove the File The Clear/Remove button doesn’t remove a successfully uploaded file from the server file system or database. It’s only removed from the file list. Remember to remove the file from the backend.

If an error or exception occurs, Upload displays a Retry button for the user to be able to try to upload the file again.

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<Upload files={files} />

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

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<Upload files={createFakeFiles()} />

Internationalization (i18n)

All labels and messages in Upload are configurable. For a complete list of them, see the API documentation (Java and Web component).

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const i18n = {
  dropFiles: {
    one: 'Raahaa tiedosto tähän',
    many: 'Raahaa tiedostot tähän',
  },
  addFiles: {
    one: 'Valitse tiedosto...',
    many: 'Valitse tiedostot...',
  },
  error: {
    tooManyFiles: 'Liian monta tiedostoa.',
    fileIsTooBig: 'Tiedosto on liian suuri.',
    incorrectFileType: 'Väärä tiedostomuoto.',
  },
  uploading: {
    status: {
      connecting: 'Yhdistetään...',
      stalled: 'Pysäytetty',
      processing: 'Käsitellään tiedostoa...',
      held: 'Jonossa',
    },
    remainingTime: {
      prefix: 'aikaa jäljellä: ',
      unknown: 'jäljellä olevaa aikaa ei saatavilla',
    },
    error: {
      serverUnavailable: 'Palvelin ei vastaa',
      unexpectedServerError: 'Palvelinvirhe',
      forbidden: 'Kielletty',
    },
  },
  units: {
    size: ['t', 'kt', 'Mt', 'Gt', 'Tt', 'Pt', 'Et', 'ZB', 'YB'],
    sizeBase: 1000,
  },
};

return <Upload i18n={i18n} />;

Customization

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

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<Upload
  maxFiles={1}
  accept="application/pdf,.pdf"
  onFileReject={fileRejectHandler}
  onMaxFilesReachedChanged={maxFilesReachedChangedHandler}
>
  <Button slot="add-button" theme="primary" disabled={maxFilesReached.current}>
    Upload PDF...
  </Button>
</Upload>

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

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<Upload>
  <Icon slot="drop-label-icon" icon="vaadin:cloud-upload-o" />
  <span slot="drop-label">
    Files will be uploaded to our cloud. See our&nbsp;
    <a href="https://vaadin.com/privacy-policy" target="_blank">
      privacy policy
    </a>
  </span>
</Upload>

Tip	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:

All Finished: Triggered when Upload has processed all of the files in its queue, regardless of whether all uploads were successful.
Failed: Occurs 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 (e.g., file size limit).
Finished: Sent when Upload receives a file, regardless of whether the upload was successful. To distinguish results, use instead either Succeeded or Failed listeners.
Progress: Event for tracking upload progress.
Started: Triggered when the upload starts.
Succeeded: Sent when the upload has been received successfully.

Best Practices

Labeling

Choose labels that are informative and instructive. 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.

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const uploadRef = useRef<any>(null);

useEffect(() => {
  if (uploadRef.current) {
    uploadRef.current.i18n.addFiles.one = 'Upload PDF...';
    uploadRef.current.i18n.dropFiles.one = 'Drop PDF here';
    uploadRef.current.i18n.error.incorrectFileType =
      'The provided file does not have the correct format (PDF document).';
    uploadRef.current.i18n = { ...uploadRef.current.i18n };
  }
}, []);

return (
  <Upload
    maxFiles={1}
    accept="application/pdf,.pdf"
    ref={uploadRef}
    onFileReject={fileRejectHandler}
  />
);

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

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const uploadRef = useRef<any>(null);

useEffect(() => {
  if (uploadRef.current) {
    uploadRef.current.i18n.addFiles.one = 'Upload Spreadsheet...';
    uploadRef.current.i18n.dropFiles.one = 'Drop spreadsheet here';
    uploadRef.current.i18n.error.incorrectFileType =
      'Provide the file in one of the supported formats (.xls, .xlsx, .csv).';
    uploadRef.current.i18n = { ...uploadRef.current.i18n };
  }
}, []);

return (
  <>
    <h4>Upload spreadsheet</h4>
    <p>
      File size must be less than or equal to {maxFileSizeInMB} MB.
      <br />
      Only Excel and CSV files are accepted.
    </p>
    <Upload
      maxFiles={1}
      maxFileSize={maxFileSizeInBytes}
      accept={acceptedTypes.join(',')}
      ref={uploadRef}
      onFileReject={(event) => {
        Notification.show(event.detail.error);
      }}
    />
  </>
);

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 and instructions on how to fix the error.

A "Server Unavailable" message might suffice for tech-savvy users, but for some it might be lacking, unhelpful, and frustrating. Error messages should be written with your users in mind.

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useEffect(() => {
  if (!uploadCaution.current || !uploadRecommended.current) {
    return;
  }

  uploadCaution.current.setupMockErrorResponse();
  uploadRecommended.current.setupMockErrorResponse();

  uploadCaution.current.i18n.uploading.error.unexpectedServerError = 'Unexpected Server Error';
  uploadCaution.current.i18n = { ...uploadCaution.current.i18n };

  uploadRecommended.current.i18n.uploading.error.unexpectedServerError =
    "File couldn't be uploaded, try again later";
  uploadRecommended.current.i18n = { ...uploadRecommended.current.i18n };
}, []);

return (
  <FormLayout responsiveSteps={layoutSteps}>
    <div>
      <strong>Caution</strong>
      <Upload ref={uploadCaution} nodrop files={createFakeFilesUploadErrorMessagesA()} />
    </div>

    <div>
      <strong>Recommended</strong>
      <Upload ref={uploadRecommended} nodrop files={createFakeFilesUploadErrorMessagesB()} />
    </div>
  </FormLayout>
);

Component for showing task completion progress.