Using Vaadin With Karaf

The Karaf http feature along with war feature provides HTTP Whiteboard implementation which is in practice the standard in Karaf. This implementation is known as PAX Web (see HTTP feature details here). PAX Web is not fully compliant to HTTP Whiteboard OSGi Compendium 7 specification: there are some issues related to ServletContextListener support. Due to these issues the recommended VaadinServlet registration way described in generic Using Vaadin with OSGi tutorial doesn’t work in PAX Web.

It’s still possible to use Vaadin OSGi support with PAX Web though. But the OSGiVaadinServlet should be used as a base class for the servlet which is registered in an OSGi bundle:

@org.osgi.service.component.annotations.Component(service = Servlet.class)
public class FixedVaadinServlet extends OSGiVaadinServlet {

    protected void servletInitialized() throws ServletException {


Refer to the generic Using Vaadin with OSGi and Using Services With Vaadin tutorials for other non-Karaf specific Vaadin OSGi documentation.

Karaf Base Starter

A Karaf base starter project is available at

The project may be used as a basis for a custom OSGi Vaadin web bundle project. The README contains information how to run Karaf, install all required Karaf features and install project feature to the existing Karaf container.

The base project generated feature Maven artifact classifier which contains all the dependencies for the project and it can be used as a basis for custom project "feature". A few Karaf features already provided by Vaadin (see below).

Karaf Features

One of the most important question which needs to be solved when OSGi bundle is deployed to the OSGi container is the bundle dependencies resolution. The bundle does not work in the OSGi container even though it’s deployed until all its dependencies are resolved. Karaf allows to solve this via "feature" concept: bundles can be combined into a "feature" which contains all dependency bundles and it can be installed as one unit.

Vaadin provides several features which can be used depending on requirements: - flow-server - flow-data - flow-osgi - flow - vaadin-core - vaadin

The flow-server feature contains the minimum dependencies which have to be added to any Vaadin web project. The flow-osgi feature contains necessary dependency for Vaadin OSGi web bundle. The flow feature combines all Flow bundles altogether and it’s convenient when you use all Flow modules in your project but it may be too big for your purposes (some bundles can be excluded from it). The similar situation is with vaadin-core and vaadin features: they combine all Flow bundles (including flow feature) plus all Vaadin components (the first one contains all free components, the second one includes free and commercial components). These features can be used as is if you want to deploy everything to the Karaf container and don’t think about anything else. But it’s also possible to use the features as a base for a custom feature.

The feature can be installed into the Karaf container via two command:

karaf@root()> feature:repo-add mvn:com.vaadin/flow/$FLOW_VERSION$/xml/features
karaf@root()> feature:install flow

Here is $FLOW_VERSION$ is a placeholder for the Flow artifact version value. The first command uses feature Maven classifier to add feature repository (which is an XML file with feature declaration). The second command installs the feature which is declared in the added repository. Here is an example of the feature repository.

The same can be done with any mentioned feature.

Sometimes it might be useful to install a bundle without a feature. This can be done this way:

karaf@root()> bundle:install mvn:com.vaadin/flow-html-components/$FLOW_VERSION$
karaf@root()> bundle:install mvn:com.vaadin/vaadin-text-field-flow/$TEXT_FIELD_VERSION$

The command refers to the Maven artifact via com.vaadin group id, flow-html-components (vaadin-text-field-flow) artifact id and the artifact version.