Spring-Rabbitmq MessageConverter - not invoking custom object handleMessage - spring

Question

I am implementing a consumer class that binds to fanout exchange in RabbitMQ and receives the message published as json. For some reason, the handleMessage within the Consumer class is not being invoked when its argument is a custom object. Same code works when the handleMessage is changed to take Object. Would appreciate your help in identity the missing piece.
Here is the configuration and consumer classes. This is not a SpringBoot application. My Configuration class has #Configuration annotation and not #SpringBootApplication.
#Bean
public SimpleMessageListenerContainer messageListenerContainer() {
SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
container.setConnectionFactory(rabbitConnectionFactory());
container.setQueueNames(QUEUE_NAME);
container.setMessageListener(listenerAdapter());
container.setMessageConverter(new Jackson2JsonMessageConverter());
container.setMissingQueuesFatal(false);
return container;
}
#Bean
public AmqpAdmin amqpAdmin() {
return new RabbitAdmin(rabbitConnectionFactory());
}
#Bean
public Queue queue() {
return new Queue(QUEUE_NAME, false, false, false);
}
#Bean
public FanoutExchange exchange() {
return new FanoutExchange(EXCHANGE_NAME, false, false);
}
#Bean
public Binding inboundEmailExchangeBinding() {
return BindingBuilder.bind(queue()).to(exchange());
}
#Bean
public ConnectionFactory rabbitConnectionFactory() {
return new CachingConnectionFactory("localhost");
}
#Bean
public RabbitTemplate rabbitTemplate() {
RabbitTemplate rabbitTemplate = new RabbitTemplate(rabbitConnectionFactory());
rabbitTemplate.setExchange(EXCHANGE_NAME);
return rabbitTemplate;
}
#Bean
MessageListenerAdapter listenerAdapter() {
return new MessageListenerAdapter(new Consumer(), "receiveMessage");
}
Here is the consumer ...
public class Consumer {
// This works
/*
public void receiveMessage(Object message) {
System.out.println("Received <" + message + ">");
}
*/
// This does not works, whereas I expect this to work.
public void receiveMessage(CustomObject message) {
System.out.println("Received <" + message + ">");
}
}
where CustomObject class is a plain POJO.
Here is an example of what is being published in RabbitMQ.
{
"state": "stable",
"ip": "1.2.3.4"
}
Its being published as json content-type
exchange.publish(message_json, :content_type => "application/json")
Appreciate all your help in making me understand the problem. Thanks.

Answer 1

The Jackson2JsonMessageConverter needs to be told what object to map the json to.
This can be provided via information in a __TypeId__ header (which would be the case if Spring was on the sending side); the header can either contain the full class name, or a token that is configured to map to the class name.
Or, you need to configure the converter with a class mapper.
For convenience there is a DefaultClassMapper that be configured with your target class:
ClassMapper classMapper = new DefaultClassMapper();
classMapper.setDefaultType(CustomObject.class);
converter.setClassMapper(classMapper);