Lazy Download Button
Lazy Download Button
This component allows you to display a normal Vaadin button to download content from your application without blocking the UI while preparing the content. This allows you to load huge files from your backend and let the browser download it when it's ready.
Please also have a look at the examples or the demo source code, if you want to see how to integrate the LDB.
Requires PUSH
Since the content preparation is done in a separate thread, this component needs Push to be activated. The component itself does not check for active Push.
Please lookup the official documentation of Vaadin on how to activate Push: https://vaadin.com/docs/flow/advanced/tutorial-push-configuration.html
Supported Vaadin versions
Please note, that I only support the latest Vaadin major version regarding bugs or feature requests. You still may use this addon for Vaadin 14+, but on your own risk. If necessary for any reason, I will update the minimal required Vaadin version.
Sample code
// Create a new instance - it needs at least a caption (or icon) and a
// callback to create the content on click time.
//
// Please be aware, that the callback is called OUTSIDE of the current UI.
// You need to use UI.access() if you want to access the UI.
LazyDownloadButton button = new LazyDownloadButton("Download", () -> {
try {
// Provide the file content as an input stream. In a WAR project, this could be for instance
return Files.newInputStream(Paths.get(getClass().getClassLoader().getResource("some-file").toURI())) } catch (IOException | InterruptedException e) {
throw new RuntimeException(e);
}
});
add(button);
// Provide a callback to create the file name on click time
LazyDownloadButton button = new LazyDownloadButton("Download",
() -> "my_file.txt",
() -> // ... create the input stream here
);
add(button);
// LDB extends Vaadin Button, so you may use a simple click listener
LazyDownloadButton button = new LazyDownloadButton(...);
button.setDisableOnClick(true);
button.addClickListener(event -> {
// show some feedback to the user, that the download is prepared in the background
event.getSource().setText("Preparing download...");
});
// LDB also provides a "download start" listener - this listener is fired, when the client
// side starts the download. Please be aware to NOT remove the button here or its content, otherwise
// the download can fail.
button.addDownloadStartsListener(event -> {
// restore normal state, so that the user can download the content again
LazyDownloadButton button = event.getSource();
button.setText("Download");
button.setEnabled(true);
});
Links
Compatibility
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Version
- Released
- 2019-11-14
- Maturity
- BETA
- License
- Apache License 2.0
Compatibility
- Framework
- Vaadin 14+
- Browser
- Browser Independent
Flow Viritin - Vaadin Add-on Directory
The commons library for Vaadin 10+. Uploads, downloads, Geolocation, forms, fieds, fluent API...
GitHub
Online Demo
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Flow Viritin version 0.5.1
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Flow Viritin version 0.5.2
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Flow Viritin version 0.7.0
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New Maven coordinates!!
in.virit:viritin:0.9.0
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Flow Viritin version 1.3.0
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Flow Viritin version 1.5.0
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Flow Viritin version 1.6.0
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Flow Viritin version 1.6.1
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Flow Viritin version 2.1.0
Improvements to work better with the "dev-bundle" in Vaadin 24+. Technically so that custom bundle is no more needed when using Viritin -> front-end build don't become any slower when dropping in this add-on.
Flow Viritin version 2.5.0
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* No extra thread created for each upload. For apps having a lot of large uploads concurrently, this might save some resources.
* Streaming now properly works in Spring Boot apps as well (doesn't use multipart request at all)
* Not extending from com.vaadin.flow.component.upload.Upload anymore, some API might be missing, please file issus for things you are missing
Flow Viritin version 2.5.1
Completely renewed UploadFileHandler component in 2.5.x series:
* The good old API that passes the [input stream for you to handle](https://vaadin.com/blog/uploads-and-downloads-inputs-and-outputs).
* No extra thread created for each upload. For apps having a lot of large uploads concurrently, this might save some resources.
* Streaming now properly works in Spring Boot apps as well (doesn't use multipart request at all). With previous version and with plain Upload you only get to access the stream once it is uploaded completely.
* The clients side opens maximum 1 server connection by default when allowing multiple files to be uploaded. This way the network/server/http2 connection don't get choked if uploading a large number of files at once.
* Not extending from com.vaadin.flow.component.upload.Upload anymore, some API might be missing, please file issus for things you are missing
Flow Viritin version 2.13.0
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Pros/cons:
* Less JVM dependencies
* Less JVM resources consumed
* More JS "dependencies"
* More browser resources consumed
* JS is loaded dynamically (to avoid requirement for custom front-end bundle) -> might cause a tiny delay for the first markdown to appear
* Tables ("non-standard markdown") supported out of the box
* Inline html not supported out of the box (default in markdown-it, doesn't sanitize the content)