无法设置@Theme vaadin

Question

I am pretty new to vaadin. I am trying to use badges. When I add the @Theme to my class:

@PageTitle("Technology")
@Route(value = "")
@Theme("common-theme")
public class TechnologyLayout extends VerticalLayout {
    ...
    var tmp = new Span(new Span(label.getName()));
    tmp.getElement().getThemeList().add("badge");
    ....
}

I get this error:

org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:165) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:577) ~[spring-context-5.3.23.jar:5.3.23]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.4.jar:2.7.4]
at com.example.demo.DemoApplication.main(DemoApplication.java:10) ~[classes/:na]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:577) ~[na:na]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.7.4.jar:2.7.4]

Caused by: org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:142) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.<init>(TomcatWebServer.java:104) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getTomcatWebServer(TomcatServletWebServerFactory.java:479) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:211) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:184) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:162) ~[spring-boot-2.7.4.jar:2.7.4]
... 11 common frames omitted

Caused by: java.lang.IllegalStateException: StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[] failed to start
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.rethrowDeferredStartupExceptions(TomcatWebServer.java:187) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:126) ~[spring-boot-2.7.4.jar:2.7.4]
... 16 common frames omitted

Process finished with exit code 0

frontend/themes/common-theme contains a theme.json as shown here :

{
  "lumoImports" : [ "typography", "color", "spacing", "badge", "utility" ]
}

Answer 1

The Theme annotation must be on a class that implements AppShellConfigurator

@Theme("common-theme")
public class AppConfiguration implements AppShellConfigurator {
}

Answer 2

Solved it by adding @Theme at the @SpringBootApplication

@SpringBootApplication
@Theme("common-theme")
public class DemoApplication extends SpringBootServletInitializer implements AppShellConfigurator {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}