Enable sending String payloads with JSON content type in SqsTemplate

[tomazfernandes]

Currently due to Spring Messaging internals if we send a String message containing a JSON without specifying a Content-Type it'll default to text/plain in the StringMessageConverter.

If we set .header(MessageHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON), it will be mapped by MappingJackson2MessageConverter which will double serialize the payload, which won't be readable.

We should look into a way of enabling users to send a String json with APPLICATION_JSON content type so it can be properly deserialized by the consumer.

[imsosleepy]

@tomazfernandes
I'm looking into this issue, but my sample code doesn't seem to be checking for this issue properly.

Below is the code I used, with some modifications from the SQS sample code in this project.

@SpringBootApplication
public class SpringSqsSample {

	private static final Logger LOGGER = LoggerFactory.getLogger(SpringSqsSample.class);

	private static final String QUEUE_NAME = "test-queue";

	public static void main(String[] args) {
		SpringApplication.run(SpringSqsSample.class, args);
	}

	@SqsListener(queueNames = QUEUE_NAME, acknowledgementMode = "ON_SUCCESS")
	void listen(Object message) {
		LOGGER.info("Received message : " + message);
	}

	@Bean
	public ApplicationRunner sendMessageToQueue2(SqsTemplate sqsTemplate) {
		String jsonString = """
			{
			  "message1": "hello",
			  "message2": "sqs!"
			}
			""";

		return args -> sqsTemplate.send(sqsTemplate.send(to -> to.queue(QUEUE_NAME).payload(jsonString).delaySeconds(30).header(MessageHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON)));
	}
}

Can you tell me if there's something wrong with my code or give me an example of a situation where it would be double serialize?