File download

In Chapter 2, Using Input Components and Forms – Time to Listen to Users, we learned how to upload files. Now we're going to learn how to download files. Let's say we have a PDF file and want users to download it by clicking a button. Doing it is quite easy. First a PDF file is a Resource, right? Suppose the file is in the classpath:

ClassResource resource = new ClassResource("enterprise-app.pdf");

We also need a Button:

Button button = new Button("Download the PDF");
button.setStyleName(BaseTheme.BUTTON_LINK);

Tip

Use button.setStyleName(BaseTheme.BUTTON_LINK) to render the button like a standard link. Next chapter we'll learn more about styles.

The following two lines will make the rest of the job:

FileDownloader downloader = new FileDownloader(resource);
downloader.extend(button);

FileDownloader is an Extension. En Extension is an interface that allows adding functionality to a component. This particular extension starts a download when the extended component is clicked. Take a...