I’ve a spring application (webservice that connect to a database and retrieve data) using a hexagonal architecture and DDD (Domain-Driven Design).
The basic struture is

Application
    Controller to webservice
    Spring security configuration
    
Domain
    Services
    Exception
    
Infrastructure
    Persistence (repository + entities)
    

I’m facing some questions related with DTO (data transfer object) layer location.

From what I understood it’s recommended to have DTOs on Application layer but it also implies to duplicate code and harder maintenance for simple project like mine.

To respect the architecture as is we’d need to follow this logic

Application
    DataController (webservice)
    DataDto
    
Domain
    DataService
    DataBean
    Mapper (to convert from DataBean to DataDto -> used by DataService)
    
    
Infrastructure
    Mapper (to convert from DataEntity to DataBean)
    DataEntity

But what if DataDto is the same as DataBean? Aren’t this counter-productive since we are duplicating code and make the maintenance harder?
It wouldn’t be better to have Dto on domain like the following?

Application
    DataController (webservice)
    
Domain
    DataService
    DataDto
    
Infrastructure
    Mapper (to convert from DataEntity to DataDto)
    DataEntity

What is the best way? Thanks for your inputs.