Spring Boot RabbitMQ Null Pointer Exception Error

Question

I am using RabbitMQ with Spring Boot to broker messages between two services. I am able to receive the message and format it but when I call a service class in the onMessage method, I get a null pointer exception error. Here is my message listener class which receives the message

public class QueueListener implements MessageListener{
    @Autowired
    private QueueProcessor queueProcessor;

    @Override
    public void onMessage(Message message) {
        String msg = new String(message.getBody());
        String output = msg.replaceAll("\\\\", "");
        String jsonified = output.substring(1, output.length()-1);

        JSONArray obj = new JSONArray(jsonified);

        queueProcessor.processMessage(obj);
    }
}

Calling the method processMessage throws null pointer exception

Can someone point to me what I ma doing wrong?

What is line 30? The queueProcessor.processMessage(obj) call? Please update your question with the full stack and configuration of the QueueProcessor — Darren Forsythe
Line 30 is queueProcessor.processMessage(obj); call. The QueueProcessor is a service class that extracts the queue JSON message from the queue and posts it to DB. I have tested that part from Postman (rest client) and its working fine — Benjamin Mwendwa Munyoki
You definitely have to show the whole stack trace. It’s not clear from here what is the problem — Artem Bilan
Best guess is you are using new QueueListener() instead of declaring it as a Spring-managed bean. Spring can only @Autowire things it knows about. If that's not it, show how you are configuring your listener container. — Gary Russell

Benjamin Mwendwa Munyoki Benjamin Mwendwa Munyoki · Accepted Answer · 2018-08-16T15:04:37

I found out the issue was in the RabbitMqConfig class. Here is the code which was causing the error:

@Configuration
public class RabbitMqConfig {
private static final String QUEUE_NAME = "my.queue.name";

    @Bean
    public ConnectionFactory connectionFactory() {
    CachingConnectionFactory connectionFactory = new CachingConnectionFactory("<url.to.rabbit>");
    connectionFactory.setUsername("<username>");
    connectionFactory.setPassword("<password>");
    return connectionFactory;;
    }

    @Bean
    public Queue simpleQueue() {
        return new Queue(QUEUE_NAME);
    }

    @Bean
    public MessageConverter jsonMessageConverter(){
        return new Jackson2JsonMessageConverter();
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        template.setRoutingKey(QUEUE_NAME);
        template.setMessageConverter(jsonMessageConverter());
        return template;
    }

    @Bean
    public SimpleMessageListenerContainer userListenerContainer() {
        SimpleMessageListenerContainer listenerContainer = new SimpleMessageListenerContainer();
        listenerContainer.setConnectionFactory(connectionFactory());
        listenerContainer.setQueues(simpleQueue());
        listenerContainer.setMessageConverter(jsonMessageConverter());
        listenerContainer.setMessageListener(new QueueListener());
        listenerContainer.setAcknowledgeMode(AcknowledgeMode.AUTO);
        return listenerContainer;
    }
}

The line listenerContainer.setMessageListener(new QueueListener()); was the source of the error. I solved it by Autowiring the class instead of using new. Here is the working code

@Configuration
public class RabbitMqConfig {
private static final String QUEUE_NAME = "my.queue.name";

    @Autowired
    private QueueListener queueListener;

    @Bean
    public ConnectionFactory connectionFactory() {
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory("<url.to.rabbit>");
        connectionFactory.setUsername("<username>");
        connectionFactory.setPassword("<password>");
        return connectionFactory;
    }

    @Bean
    public Queue simpleQueue() {
        return new Queue(QUEUE_NAME);
    }

    @Bean
    public MessageConverter jsonMessageConverter(){
        return new Jackson2JsonMessageConverter();
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        template.setRoutingKey(QUEUE_NAME);
        template.setMessageConverter(jsonMessageConverter());
        return template;
    }

    /*@Bean
    public SimpleMessageListenerContainer userListenerContainer() {
        SimpleMessageListenerContainer listenerContainer = new SimpleMessageListenerContainer();
        listenerContainer.setConnectionFactory(connectionFactory());
        listenerContainer.setQueues(simpleQueue());
        listenerContainer.setMessageConverter(jsonMessageConverter());
        listenerContainer.setMessageListener(queueListener);
        listenerContainer.setAcknowledgeMode(AcknowledgeMode.AUTO);
        return listenerContainer;
    }
}

Hope this helps someone else

Spring Boot RabbitMQ Null Pointer Exception Error

2 Answers