Axon Framework provides extensive support for Spring, but does not require you to use Spring in order to use Axon. All components can be configured programmatically and do not require Spring on the classpath. However, if you do use Spring, much of the configuration is made easier with the use of Spring's annotation support. Axon provides Spring Boot starters on the top of that, so you can benefit from auto-configuration as well.
Axon's Spring Boot auto-configuration is by far the easiest option to get started configuring your Axon components. By simply declaring dependency to
axon-spring-boot-starter, Axon will automatically configure the infrastructure components (command bus, event bus, query bus), as well as any component required to run and store aggregates and sagas.
With a lot of things happening in the background, it sometimes becomes difficult to understand how an annotation or just including a dependency enables so many features.
axon-spring-boot-starter follows general Spring boot convention in structuring the starter. It depends on
axon-spring-boot-autoconfigure which holds concrete implementation of Axon auto-configuration. When Axon Spring Boot application starts up, it looks for a file named
spring.factories in the
classpath. This file is located in the
META-INF directory of
This file maps different configuration classes which Axon Spring boot application will try to apply. So, as per this snippet, Spring Boot will try to apply all the configuration classes for
Whether these configuration classes will be applied or not, it will depend on conditions defined on this classes:
AxonServerAutoConfiguration configures Axon Server as implementation for the Command Bus, Query Bus and Event Store. It will be applied before
AxonAutoConfiguration, and it will be applied only if the
org.axonframework.axonserver.connector.AxonServerConfiguration class is available in the classpath. Axon Server auto configuration can be disabled by setting the
axon.axonserver.enabled property to
false in the
AxonAutoConfiguration configures a 'non-axon-server' implementation of Command Bus, Query Bus, Event Store/Event Bus and other Axon components. These components will be initialized only if they are not in the Spring Application context already, eg.
AxonAutoConfiguration will be applied after
AxonServerAutoConfiguration these Axon components will be in the Spring Application Context already, and therefore Axon Server's implementation of Command Bus, Query Bus and Event Store/Event Bus will win.
Axon Spring Boot auto-configuration is not intrusive. It will define only Spring components that you haven't already explicitly defined in the application context. This allow you to completely override the auto-configured beans by defining your own in one of the
Specific Axon (Spring) component configurations will be explained in detail in the following sections of this guide.
Spring Boot Developer Tools Notice
Spring Boot Developer Tools are a nifty addition to your project to enhance the developer experience. However, introducing
spring-boot-devtoolsinto your project will impose some class loading operations which have shown not to work all to well with Axon Framework. We are aware of the situation and on the look out for a solution.
In the meantime we suggest not to include
spring-boot-devtoolswhen developing an Axon application.