Package org.axonframework.messaging.commandhandling.distributed

Class DistributedCommandBus

java.lang.Object
org.axonframework.messaging.commandhandling.distributed.DistributedCommandBus
All Implemented Interfaces:
DescribableComponent, CommandBus, CommandHandlerRegistry<CommandBus>
public class DistributedCommandBus extends Object implements CommandBus
Implementation of a CommandBus that is aware of multiple instances of a CommandBus working together to spread load.

Each "physical" CommandBus instance is considered a "segment" of a conceptual distributed CommandBus.

The DistributedCommandBus relies on a CommandBusConnector to dispatch commands and replies to different segments of the CommandBus. Depending on the implementation used, each segment may run in a different JVM.

Since:
2.0.0
Author:
Allard Buijze

  • Constructor Details

    • DistributedCommandBus

      public DistributedCommandBus(@Nonnull CommandBus localSegment, @Nonnull CommandBusConnector connector, @Nonnull DistributedCommandBusConfiguration configuration)
      Constructs a DistributedCommandBus using the given localSegment for subscribing handlers and the given connector to dispatch commands and replies to different segments of the CommandBus.
      Parameters:
      localSegment - The localSegment CommandBus used to subscribe handlers to.
      connector - The Connector to dispatch commands or replies.
      configuration - The DistributedCommandBusConfiguration containing the load factor and the ExecutorServiceFactory for this bus.

  • Method Details

    • subscribe

      public DistributedCommandBus subscribe(@Nonnull QualifiedName name, @Nonnull CommandHandler handler)
      Description copied from interface: CommandHandlerRegistry
      Subscribe the given handler for commands of the given name.

      If a subscription already exists for the name, the behavior is undefined. Implementations may throw an exception to refuse duplicate subscription or alternatively decide whether the existing or new handler gets the subscription.

      Specified by:
      subscribe in interface CommandHandlerRegistry<CommandBus>
      Parameters:
      name - The name the given commandHandler can handle.
      handler - The handler instance that handles commands for the given name.
      Returns:
      This registry for fluent interfacing.

    • dispatch

      public CompletableFuture<CommandResultMessage> dispatch(@Nonnull CommandMessage command, @Nullable ProcessingContext processingContext)
      Description copied from interface: CommandBus
      Dispatch the given command to the command handler subscribed to the given command's name. The name is typically deferred from the Message.type(), which contains a MessageType.qualifiedName().
      Specified by:
      dispatch in interface CommandBus
      Parameters:
      command - The command to dispatch.
      processingContext - The processing context under which the command is being published (can be null).
      Returns:
      The CompletableFuture providing the result of the command, once finished.

    • describeTo

      public void describeTo(@Nonnull ComponentDescriptor descriptor)
      Description copied from interface: DescribableComponent
      Describe the properties of this DescribableComponent with the given descriptor.

      Components should call the appropriate describeProperty methods on the descriptor to register their properties. The descriptor is responsible for determining how these properties are formatted and structured in the final output.

      Best Practices: As a general rule, all relevant fields of a DescribableComponent implementation should be described in this method. However, developers have discretion to include only the fields that make sense in the context. Not every field may be meaningful for description purposes, especially internal implementation details. Furthermore, components might want to expose different information based on their current state. The final decision on what properties to include lies with the person implementing the describeTo method, who should focus on providing information that is useful for understanding the component's configuration and state.

      Example implementation: 

       public void describeTo(ComponentDescriptor descriptor) {
     descriptor.describeProperty("name", this.name);
     descriptor.describeProperty("enabled", this.enabled);
     descriptor.describeProperty("configuration", this.configuration); // A nested component
     descriptor.describeProperty("handlers", this.eventHandlers);      // A collection
 }
      Specified by:
      describeTo in interface DescribableComponent
      Parameters:
      descriptor - The component descriptor to describe this DescribableComponentn its properties in.