cqrs

CQRS Pattern for Spring Boot BFF

Note: This BFF project orchestrates HTTP calls to backend services and does NOT use database transactions. Therefore, @Transactional annotations are NOT used in handlers.

Core Interfaces (Located in application/cqrs/)

// Marker interface for commands (write operations)
public interface Command<T> {}

// Marker interface for queries (read operations)
public interface Query<T> {}

// Command handler
public interface CommandHandler<C extends Command<T>, T> {
    T handle(C command);
}

// Query handler
public interface QueryHandler<Q extends Query<T>, T> {
    T handle(Q query);
}

// Dispatcher interface
public interface Dispatcher {
    <T> T dispatch(Command<T> command);
    <T> T dispatch(Query<T> query);
}

SimpleDispatcher Implementation

@Service
public class SimpleDispatcher implements Dispatcher {
    
    private final ApplicationContext context;
    
    public SimpleDispatcher(ApplicationContext context) {
        this.context = context;
    }
    
    @Override
    @SuppressWarnings("unchecked")
    public <T> T dispatch(Command<T> command) {
        var handlerType = getHandlerType(CommandHandler.class, command.getClass());
        var handler = (CommandHandler<Command<T>, T>) context.getBean(handlerType);
        return handler.handle(command);
    }
    
    @Override
    @SuppressWarnings("unchecked")
    public <T> T dispatch(Query<T> query) {
        var handlerType = getHandlerType(QueryHandler.class, query.getClass());
        var handler = (QueryHandler<Query<T>, T>) context.getBean(handlerType);
        return handler.handle(query);
    }
    
    private Class<?> getHandlerType(Class<?> handlerInterface, Class<?> messageType) {
        // Finds handler bean by matching generic type parameter
        return context.getBeansOfType(handlerInterface).values().stream()
            .map(Object::getClass)
            .filter(type -> matchesMessageType(type, handlerInterface, messageType))
            .findFirst()
            .orElseThrow(() -> new IllegalStateException(
                "No handler found for " + messageType.getSimpleName()));
    }
}