ribbon.js | 1kb javascript gist to generate a ribbon in your website | Canvas library

What happens here is caused by a security feature. Since the files are in this case served directly from the classpath, Vaadin takes some precautions to prevent accidentally also publishing other things from the classpath, e.g. something like DatabaseConnection.java which might contain sensitive passwords.

For this reason, only files that are explicitly published using a @StyleSheet, @JavaScript or @HtmlImport annotation are available. Since there is no corresponding annotation for e.g. css/images/AllShapes.png, the server ignores those requests.

I'm aware of a couple of potential workarounds in this kind of case, but neither is really elegant:

1. Put the images in e.g. VAADIN/css/images and update the CSS to use an appropriate number of ../ segments to cancel out the /APP/PUBLISHED/ part of the URL. The URL in the CSS would thus be something along the lines of ../../VAADIN/css/images.AllShapes.png.
2. Put the CSS along with the images in VAADIN/. In that way, you don't need to change the URLs that refer to the images, but you instead need to manually load the CSS instead of relying on the convenient @StyleSheet annotation. In that case, I'd recommend using something like ui.getPage().getStyles().add(new ThemeResource("../../css/name.css"));. The ../../ part is to cancel out themes/mytheme/ that will automatically be used for a theme resource. You could do this in e.g. the attach() method (just remember to also call super.attach()). You should preferably also add some logic that only adds the dependency if it hasn't already been done previously for the same UI instance.
3. Use the internal LegacyCommunicationManager.registerDependency method to also register your images to be available directly from the classpath. You can find an instance to LegacyCommunicationManager using vaadinSession.getCommunicationManager().

As an unrelated note, I'd recommend combining the different scripts and CSS files into a single file of each type. The reason for this is that loading lots of small files over HTTP causes some performance overhead that can be avoided by bundling the files together.

executionContext is a reference to the save event. You modify your addOnStageChange callback function to receive the stage context