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Step 3 - Running a Spring Boot application with MPR and Flow

Note
 This step is needed in case your Vaadin 7 or 8 application uses Spring Boot. If it isn’t the case, go back to the framework selection.

Updating to the correct Spring version

Update parent org.springframework.boot:spring-boot-starter-parent to 2.1.7.RELEASE or newer.

The dependency com.vaadin:vaadin-spring-boot-starter shouldn’t have a version defined as it comes from vaadin-bom.

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.6.RELEASE</version>
</parent>

<dependency>
    <groupId>com.vaadin</groupId>
    <artifactId>vaadin-spring-boot-starter</artifactId>
</dependency>
Note
 Also take a look at the Using Vaadin with Spring Boot tutorial on how Flow integrates with Spring.

Handling of SpringUI

The @SpringUI can be replaced with a @Route. For example this UI:

@SpringUI
@Theme("valo")
public class TodoUI extends UI {
    @Override
    protected void init(VaadinRequest vaadinRequest) {
        setContent(new HorizontalLayout());
    }
}

Can be replaced with:

@Route("")
public class TodoUI extends Div implements HasLegacyComponents {
    @PostConstruct
    private void buildLayouts() {
        setSizeFull();
        add(new HorizontalLayout());
    }
}
Note
 Annotations in the UI, such as @Theme and @Title and so on, are dealt with later on in the tutorial. Most of them have similar counterpart in either Flow or MPR.

Update imports

Then any com.vaadin.spring.annotation imports needs to be changed to com.vaadin.flow.spring.annotation.

Note
 The V14 Spring add-on doesn’t have a feature comparable with ViewScope

What to do with SpringView

Any @SpringView should be updated to a Flow Route by wrapping them as a MprRouteAdapter<? extends View> or re-writing it to be a Flow Component. See Upgrading Views to Flow Routes for details.

The easiest way to migrate a Spring view is to wrap it in a component that extends MprRouteAdapter<? extends View> and then define a navigation target for it with @Route. No other annotation for the wrapper component or the wrapped view is needed. Starting from Vaadin 21, @RouteScope without @RouteScopeOwner annotation can be used as a replacement for @ViewScope. The bean within @RouteScope (without specified @RouteScopeOwner) stays preserved until the current navigation target/view is active (attached). It’s possible to use @RouteScopeOwner explicitly, but that requires an extra line.

The following is an example of using @RouteScope:

@Route("help")
public class HelpRoute extends MprRouteAdapter<HelpView>  {
}

public class HelpView extends VerticalLayout implements View {

    @Autowired
    private ApplicationContext context;

    @Override
    public void enter(ViewChangeEvent event) {
       HelpService service = context.getBean(HelpService.class);
       // every time when {@code context.getBean(HelpService.class)} called
       // the HelpService instance is the same until we're inside HelpView/HelpRoute
       Label label = new Label(service.getHelp());
       addComponent(label);
    }
}

@RouteScope
public class HelpService {

    public String getHelp(){
        return "some help";
    }
}

Things to keep in mind

  • When porting the UI to a flow component, you lose the ability to use UI methods, such as setErrorHandler. You can still access those by using UI.getCurrent(). The method setContent isn’t supported though - you should use the add method from your Flow layout instead.

  • When running MPR with Spring, the Spring integration is done with Flow (and not anymore with Vaadin 7 or 8), so sometimes you need to import classes from the old vaadin-spring project to make your MPR project to compile, since those classes aren’t present anymore in the new versions of vaadin-spring. The source code of vaadin-spring can be found on GitHub. Examples of such classes:

    • com.vaadin.spring.access.SecuredViewAccessControl;

    • com.vaadin.spring.access.ViewAccessControl;

    • com.vaadin.spring.internal.SpringBeanUtil;

    • com.vaadin.spring.internal.VaadinSpringComponentFactory;

    • com.vaadin.spring.server.SpringVaadinServletService;

  • If your routes are defined in a different package than the Spring application itself, you need to annotate your application with @EnableVaadin, to Spring to scan the appropriate folders for beans. For example:

// Assuming that Application is in a different package than the classes
// annotated with @Route
@SpringBootApplication
@EnableVaadin("com.mycompany.views")
public class Application extends SpringBootServletInitializer {

Next step

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