Spring Boot Rabbitmq AMQP & WebSocket NULL pointer exception

Question

I'm trying to send a message with a Rabbitmq in WebSocketHandler, right after the user's connection establishes. The problem is, that the Rabbitmq producer bean is null. Calling a producer from the Controller works perfectly fine, but when i try to call it from the WebSocketHandler bean, if fails with NULL pointer exception:

WebSocket configuration:

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {


public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(new MyWebSocketHandler(), "/connect");
}

}

WebSocket handler bean, where the NULL pointer exceptions heppens:

@Component
public class MyWebSocketHandler extends TextWebSocketHandler {
private static final Logger LOG = LoggerFactory.getLogger(WebSocketConfig.class);

@Autowired
QueueProducer producer; //NULL

List<WebSocketSession> sessions = new CopyOnWriteArrayList<>();

    @Override
    public void afterConnectionEstablished(WebSocketSession session) throws Exception {
    sessions.add(session);
    List<String> lol = session.getHandshakeHeaders().get("User-Agent");
    //Calling the rabbitmq producer
    producer.produce("Hi Mark");//NULL
}

Rabbitmq config:

@Configuration
public class RabbitConfiguration {

@Value("${fanout.exchange}")
private String fanoutExchange;

@Value("${queue.name}")
private String queueName;

@Bean
Queue queue() {
return new Queue(queueName, true);
}

@Bean
FanoutExchange exchange() {
return new FanoutExchange(fanoutExchange);
}

@Bean
Binding binding(Queue queue, FanoutExchange exchange) {
return BindingBuilder.bind(queue).to(exchange);
}

}

Rabbitmq producer code:

@Component
public class QueueProducer {

protected Logger logger = LoggerFactory.getLogger(getClass());

@Value("${fanout.exchange}")
private String fanoutExchange;

private final RabbitTemplate rabbitTemplate;

@Autowired
public QueueProducer(RabbitTemplate rabbitTemplate) {
    super();
    this.rabbitTemplate = rabbitTemplate;
}

public void produce(String message) throws Exception {
    logger.info("Storing notification...");
    rabbitTemplate.setExchange(fanoutExchange);
    rabbitTemplate.convertAndSend(message);
    logger.info("Notification stored in queue sucessfully");
}

}

Stack Trace:

java.lang.NullPointerException: null
at com.ta9.common.Config.MyWebSocketHandler.afterConnectionEstablished(MyWebSocketHandler.java:43) ~[classes/:na]
at org.springframework.web.socket.handler.WebSocketHandlerDecorator.afterConnectionEstablished(WebSocketHandlerDecorator.java:70) ~[spring-websocket-5.3.8.jar:5.3.8]
at org.springframework.web.socket.handler.LoggingWebSocketHandlerDecorator.afterConnectionEstablished(LoggingWebSocketHandlerDecorator.java:48) ~[spring-websocket-5.3.8.jar:5.3.8]
at org.springframework.web.socket.handler.ExceptionWebSocketHandlerDecorator.afterConnectionEstablished(ExceptionWebSocketHandlerDecorator.java:48) ~[spring-websocket-5.3.8.jar:5.3.8]
at org.springframework.web.socket.adapter.standard.StandardWebSocketHandlerAdapter.onOpen(StandardWebSocketHandlerAdapter.java:104) ~[spring-websocket-5.3.8.jar:5.3.8]
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:135) ~[tomcat-embed-websocket-9.0.48.jar:9.0.48]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:940) ~[tomcat-embed-core-9.0.48.jar:9.0.48]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1723) ~[tomcat-embed-core-9.0.48.jar:9.0.48]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.48.jar:9.0.48]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.48.jar:9.0.48]
at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

Thank you in advance.

Answer 1

That's expected behavior. Let's see to your code one more time:

registry.addHandler(new MyWebSocketHandler(), "/connect");

You see you do new manually. You don't rely on dependency injection container over here. Your MyWebSocketHandler is not a bean in this case. Since it is marked as a @Component I suppose it is scanned properly and made it available as a bean into an application context. So, probably you can do like this to fix your problem:

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

    @Autowired
    MyWebSocketHandler myWebSocketHandler;
   
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(this.myWebSocketHandler, "/connect");
    }

}