Adding additional HTTP headers with JAX-RS and Bean Validation

A JAX-RS resource with input validation:

@Stateless
@Path("ping")
@Consumes(MediaType.TEXT_PLAIN)
@Produces(MediaType.TEXT_PLAIN)
public class PingResource {

    @GET
    public String ping() {
        System.out.println(".");
        return "Enjoy Jakarta EE 8!";
    }

    @POST
    public void save(@Size(min = 2, max = 3) String ping) {
    }
}    

import java.util.stream.Collectors;
import javax.validation.ConstraintViolationException;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;

@Provider
public class ContraintViolationMapper implements ExceptionMapper<ConstraintViolationException> {

    @Override
    public Response toResponse(ConstraintViolationException exception) {
        String messages = exception.getConstraintViolations().stream().
                map(v -> v.getMessage()).
                collect(Collectors.joining(","));
        return Response.status(400).header("reason", messages).build();
    }

}

...will return additional information in header on each contraint violation.

A failed input validation: curl -XPOST -i -H"Content-type: text/plain" -d'duke' http://localhost:8080/jaxrs-beanvalidation/resources/ping mainifests as:

HTTP/1.1 400 Bad Request
Server: Payara Server  5.184 #badassfish
reason: size must be between 2 and 3
(...)

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