Command Processing

This page provides specifics around tuning the command processing within an Axon application.‌

Duplicate Command Handler Registration

As described in the Messaging Concepts page, a command is always routed to a single destination. This means that during the registration of a command handler within a given JVM, a second registration of an identical command handler method should be dealt with in a desirable manner.‌

How an Axon application reacts to such a duplicate registration is defined by the DuplicateCommandHandlerResolver. This resolver is a functional interface ingesting a command name and a registered candidate command handler method; a single command handler method is the return value. By default, the LoggingDuplicateCommandHandlerResolver is used, which will log a warning and returns the candidate handler.‌

To configure the used DuplicateCommandHandlerResolver it is suggested to use the DuplicateCommandHandlerResolution, as this class gives a handle to all provided implementations. To configure the duplicate resolver to, for example, throw a DuplicateCommandHandlerSubscriptionException as a warning, the following approach can be taken:

Axon Configuration API

Somewhere in a configuration class:

DefaultConfigurer.defaultConfiguration().registerComponent(
    DuplicateCommandHandlerResolution.class,
    config -> DuplicateCommandHandlerResolution.rejectDuplicates()
);

Spring Boot Auto Configuration

Somewhere in a configuration class:

@Bean
public DuplicateCommandHandlerResolver duplicateCommandHandlerResolver() {
    return DuplicateCommandHandlerResolution.rejectDuplicates();
}