How to modify spring-websocket to interface with broker via MQTT instead of STOMP?

Question

I'm building a spring-websocket application that currently uses RabbitMQ as a message broker via the STOMP protocol. The rest of our organization mostly uses IBM Websphere MQ as a message broker, so we'd like to convert it away from RabbitMQ. However Websphere MQ doesn't support the STOMP protocol, which is spring-websocket's default. MQTT seems like the easiest supported protocol to use instead. Ideally our front-end web clients will continue to use STOMP, but I'm also OK with migrating them to MQTT if needed.

What classes do I need to overwrite to make spring-websocket interface with the broker via MQTT instead of STOMP? This article provides some general guidance that I should extend AbstractMessageBrokerConfiguration, but I'm unclear where to begin.

Currently I'm using the standard configuration methods: registry.enableStompBrokerRelay and registerStompEndpoints in AbstractWebSocketMessageBrokerConfigurer

Answer 1

Ryan has some good pointers.

The main work is going to be creating a replacement for StompBrokerRelayMessageHandler with an MqttBrokerMessageHandler that not only talks to an MQTT broker but also adapts client STOMP frames to MQTT and vice versa. The protocols are similar enough that it may be possible to find common ground but you won't know until you try.

Note that we did have plans for for MQTT support https://jira.spring.io/browse/SPR-12581 but the key issue was that SockJS which is required over the Web for fallback support does not support binary messages.