CQRS and Commands Java + Spring similar to MediatR

Question

While working on a .NET project I come across a library MediatR which made CQRS and Commands simple to implement. I really like using commands and commands handlers as I've worked on far too many projects that have giant procedural style service classes that inject way to many dependencies making unit testing painful. I am looking for something similar to MediatR for Spring + Java. Essentially I would like to inject a single dependency into the controller class and have it delegate commands to the appropriate command handler. I provided a few snippets of what MediatR looks like below. I prefer the way mediator does it as injecting the CommandHandlers into the controller class can lead to the same issue with the class having tons of dependencies injected.

I've came across this library but it seems more like a side project that something that is production ready. https://github.com/sleroy/spring-cqrs-arch. I am aware of the Axon framework, but I'm not looking to go full blown event sourcing at this point. Are there any libraries out there already for this that maybe I'm haven't stumbled across yet? I suppose I could just use the Guava EventBus.

Below is a C# example of what MediatR usage looks like.

Controller

namespace DAB.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class PersonController : ControllerBase
    {
        private readonly IMediator mediator;

        public PersonController(IMediator mediator)
        {
            this.mediator = mediator;
        }

        // GET api/values
        [HttpPut("{id}/changename")]
        public async Task<ActionResult> ChangeName([FromBody] ChangeNameCommand command)
        {
            await this.mediator.Send(command);
            return Ok();
        }
    }
}

Command

public class ChangeNameCommand: IRequest<bool>
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

CommandHandler

public class ChangeNameHandler: IRequestHandler<ChangeNameCommand, bool>
{
    public Task<bool> Handle(ChangeNameCommand request, CancellationToken cancellationToken)
    {
        Console.WriteLine($"Changing name to {request.FirstName} {request.LastName}");
        return Task.FromResult(true);
    }
}

Answer 1

Check out PipelinR. It's 15KB, zero-dependency library, with a nice Spring and Spring Boot integration.