使用带有Spring Boot的Java API for WebSocket(JSR-356)

Question

我是Spring的新手(并在stackoverflow上提问).

我想通过Spring Boot启动嵌入式(Tomcat)服务器并向其注册JSR-356 WebSocket端点.

这是主要方法:

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

这是配置的外观:

@Configuration
public class EndpointConfig {

    @Bean
    public EchoEndpoint echoEndpoint() {
        return new EchoEndpoint();
    }

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

该EchoEndpoint实施是直截了当:

@ServerEndpoint(value = "/echo", configurator = SpringConfigurator.class)
public class EchoEndpoint {

    @OnMessage
    public void handleMessage(Session session, String message) throws IOException {
        session.getBasicRemote().sendText("echo: " + message);
    }
}

对于第二部分,我已经关注了这篇博文:https://spring.io/blog/2013/05/23/spring-framework-4-0-m1-websocket-support.

但是,当我运行应用程序时,我得到:

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

异常是由NullPointerExceptionin 进一步引起的ServerEndpointExporter,因为返回的getServletContext方法applicationContext仍然null在这一点上.

有更好理解Spring的人可以帮助我吗？谢谢!

Answer 1

ServerEndpointExporter对使用Spring Boot时不适用的应用程序上下文的生命周期做出一些假设.具体来说,它假定当setApplicationContext被调用时,调用getServletContext上ApplicationContext会返回一个非空值.

您可以通过替换来解决此问题:

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

附:

@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);
            }               
        }           
    };
}

这推迟了处理直到servlet上下文可用.

更新:您可能希望观看SPR-12109.一旦修复,就不再需要上述解决方法.