Vaadin 8 - Download Button for a text file with String content - scala

Question

I want to assign String content to a variable and enable the user to download that String as a text file.
I know there is FileDownloader from Vaadin 8 which I can use but I don't want static file/image download capability but rather dynamic String content which can downloaded a text file in the browser.

Answer 1

The resource interface in Vaadin, that is used by FileDownloader is a bit cumbersome. Especially so for dynamically created content, whose generation you'll want to postpone until user actually clicks the download button, which is very common in typical Vaadin apps.
Viritin add-on
Thus, I suggest to add Viritin add-on to your application. Use the DownloadButton component from it, which simplifies the usage a lot.
Here is a trivial example:
DownloadButton simple = new DownloadButton(out -> {
try {
out.write("Foobar".getBytes());
} catch (IOException ex) {
// exception handling
}
}).withCaption("Simple Download");
To see more complete example, refer to the tests in the Viritin project. From the project you can also see the "raw solution" if you peruse the source code of DownloadButton class.
PS. I'm the author of Viritin, so kind of biased to suggest its usage, but I have also been working with Vaadin for Vaadin Ltd for over a decade.

Answer 2

Here's a simple solution in Scala. We create a ReportDownloader component which extends VerticalLayout. It contains a "Download" button which trigger text file download in the browser.
import com.vaadin.ui.{Button, VerticalLayout}
import com.vaadin.server._
import java.io.{ByteArrayInputStream}
class VaadinStringStream(str : String, browserFileNameSuggestion : String) extends ConnectorResource {
override def getMIMEType: String = "text/plain"
override def getFilename: String = browserFileNameSuggestion
override def getStream: DownloadStream = new DownloadStream(
new ByteArrayInputStream(str.getBytes), getMIMEType, getFilename
)
}
class ReportDownloader extends VerticalLayout{
val btn = new Button("DOWNLOAD")
this addComponent btn
val stream = new VaadinStringStream("This is a sample txt file content", "report.txt")
new FileDownloader(stream).extend(btn)
}
VaadinStringStream takes dynamic String content and a suggested filename for the browser as arguments.