Using Java API for WebSocket (JSR-356) with Spring Download

Question

I am new to Spring (and asking questions about stackoverflow).

I would like to start the embedded (Tomcat) server through Spring Boot and register the WebSocket JSR-356 endpoint.

This is the main method:

@ComponentScan @EnableAutoConfiguration public class Server { public static void main(String[] args) { SpringApplication.run(Server.class, args); } } 

This is what the configuration looks like:

 @Configuration public class EndpointConfig { @Bean public EchoEndpoint echoEndpoint() { return new EchoEndpoint(); } @Bean public ServerEndpointExporter endpointExporter() { return new ServerEndpointExporter(); } } 

EchoEndpoint implementation is straightforward:

 @ServerEndpoint(value = "/echo", configurator = SpringConfigurator.class) public class EchoEndpoint { @OnMessage public void handleMessage(Session session, String message) throws IOException { session.getBasicRemote().sendText("echo: " + message); } } 

In the second part, I followed this blog post: https://spring.io/blog/2013/05/23/spring-framework-4-0-m1-websocket-support .

However, when I launch the application, I get:

 Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'endpointExporter' defined in class path resource [hello/EndpointConfig.class]: Initialization of bean failed; nested exception is java.lang.IllegalStateException: Failed to get javax.websocket.server.ServerContainer via ServletContext attribute 

Also, the exception is thrown by a NullPointerException in ServerEndpointExporter because the getServletContext method in applicationContext returns still null at this point.

Can someone with a better understanding of Spring help me? Thanks!

Answer 1

ServerEndpointExporter makes some assumptions about the application context life cycle that fails when you use Spring Boot. In particular, it is assumed that, when calling setApplicationContext calling getServletContext ApplicationContext return a nonzero value.

You can work around the problem by replacing:

 @Bean public ServerEndpointExporter endpointExporter() { return new ServerEndpointExporter(); } 

WITH

 @Bean public ServletContextAware endpointExporterInitializer(final ApplicationContext applicationContext) { return new ServletContextAware() { @Override public void setServletContext(ServletContext servletContext) { ServerEndpointExporter serverEndpointExporter = new ServerEndpointExporter(); serverEndpointExporter.setApplicationContext(applicationContext); try { serverEndpointExporter.afterPropertiesSet(); } catch (Exception e) { throw new RuntimeException(e); } } }; } 

Rejects processing until a servlet context is available.

Refresh . You may like to watch SPR-12109 . After fixing the workaround described above, it is no longer required.