Servlets and UIs

A Vaadin application in its simplest form is a Servlet that delegates user interface logic to a UI implementation. The vaadin-server dependency includes the Servlet implementation: the VaadinServlet class. Let’s configure one.

Create a new directory with the name java inside the src/main directory.

You might have to tell your IDE that this is a source directory. You will most likely find this by right-clicking the directory and selecting the option to mark it as a source directory. Check the documentation for your IDE for detailed instructions.

Create a new package with the name packt.vaadin.datacentric.chapter01, and add a simple UI implementation inside this package:

public class VaadinUI extends UI {

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        setContent(new Label("Welcome to Data-Centric Applications with Vaadin 8!"));
    }
}

Add a new WebConfig class to encapsulate everything related to web configuration, and define the VaadinServlet as an inner class:

public class WebConfig {

    @WebServlet("/*")
    @VaadinServletConfiguration(
          ui = VaadinUI.class, productionMode = false)
    public static class WebappVaadinServlet extends VaadinServlet {
    }
}

The WebappVaadinServlet class must be public static to allow its instantiation by the Servlet Container. Notice how we are configuring /* as the servlet URL mapping using the @WebServlet annotation. This makes the application available at the root of the deployment path. Notice also how the @VaadinServletConfiguration annotation connects the Servlet to the UI implementation, the VaadinUI class we implemented in the previous step.