spring-boot-starter-websocket doesn't work in standalonemode

[BigMichi1]

I have an application defined this way:

@ComponentScan
@Configuration
@EnableAutoConfiguration
public class Application extends SpringBootServletInitializer {
    private static final Class<Application> APPLICATION_CLASS = Application.class;

    public static void main(final String[] args) {
        SpringApplication.run(APPLICATION_CLASS, args);
    }

    @Override
    protected SpringApplicationBuilder configure(final SpringApplicationBuilder application) {
        return application.sources(APPLICATION_CLASS);
    }
}

and a ServerEndpoint:

@ServerEndpoint(value = "/websocket")
public class WebSocketTest {
    private static Set<Session> clients = Collections.synchronizedSet(new HashSet<Session>());

    @OnMessage
    public void onMessage(String message, Session session) throws IOException {
        synchronized (clients) {
            for (Session client : clients) {
                if (!client.equals(session)) {
                    client.getBasicRemote().sendText(message);
                }
            }
        }
    }

    @OnOpen
    public void onOpen(Session session) {
        clients.add(session);
    }

    @OnClose
    public void onClose(Session session) {
        clients.remove(session);
    }
}

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>websocket</groupId>
    <artifactId>websocket</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.0.M1</version>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

now when i run this war as a standalone application i am unable to connect to the websocket, when i deploy this war to a standalone tomcat connection can be successfull established. there seems to be something missing in the embedded configuration when using websockets in standalone mode

[wilkinsona]

Tomcat uses a ServletContainerInitializer to find classes annotated with @ServerEndpoint. Spring Boot doesn't support ServerContainerInitializerswhen you're using an embedded web container (see #321 for more details).

You need to make all of your endpoints Spring beans and use Spring's ServerEndpointExporter instead. Unfortunately, there's a bug that stops the exporter from working out-of-the-box with Spring Boot. There's a workaround, however. Add the following bean to Application:

    @Bean
    public ServletContextAware endpointExporterInitializer(final ApplicationContext applicationContext) {
        return new ServletContextAware() {
            @Override
            public void setServletContext(ServletContext servletContext) {
                ServerEndpointExporter exporter = new ServerEndpointExporter();
                exporter.setApplicationContext(applicationContext);
                exporter.afterPropertiesSet();
            }
        };
    }

[wilkinsona]

I've seen this a few times now. At the least we should document the behaviour difference and what to do in the embedded case.

[wilkinsona]

I've now realised that the workaround is only viable as long as you're not trying to use ServerEndpointConfig beans. ServerEndpointExporter needs to be exposed as a Bean in the application context for that to work as they're processed as part of ServerEndpointExporter's implementation of the BeanPostProcessor contract