Broker Api Redesign

HAPI-FHIR requires a message broker to provide asynchronous messaging services for

• subscription processing
• mdm processing
• batch processing

Prior to HAPI version 8.2.0, HAPI-FHIR's broker api was built on top of Spring Messaging, a Spring API for JMS, a 1990s Java API for asynchronous message processing. HAPI ships with the simple Spring in-memory implementation of this API.

Since that time, a number of new message broker paradigms have emerged that have moved the industry away from JMS.

In release 8.2.0, HAPI-FHIR decouples the message broker services from Spring Messaging. SpringMessaging adapters are provided for backwards compatibility.

The new API largely mirrors with Spring Messaging API, with a few important differences. Here is a mapping from the old API to the new API.

Old	New	Notes
ca.uhn.fhir.jpa.subscription.channel.api.IChannelFactory	ca.uhn.fhir.broker.api.IBrokerClient	Creates producers and consumers
org.springframework.messaging.MessageHandler	ca.uhn.fhir.broker.api.IMessageListener	In the new API Consumers and Listeners are always one-to-one
org.springframework.messaging.Message	ca.uhn.fhir.rest.server.messaging.IMessage	ResourceModifiedJsonMessage used to inherit from Message now it inherits from IMessage
IChannelReceiver	IChannelConsumer	IChannelConsumer are now always created with exactly one message listener