How to return a string in response that have @Produces(MediaType.APPLICATION_JSON)?

@GET
@Path("/paises/{id}")
@Produces(MediaType.APPLICATION_JSON)
public Response findCountryList(@PathParam("id")int id){
    try{
    ArrayList<Country> lista = new ArrayList<>();
    for(int i=0; i<10 ;i++){
        Country c = new Country();
        c.setId(i);
        c.setName("country"+i);
        c.setCode("countryIsoCode"+i);
        c.setRegion("region"+i);
        lista.add(c);
        }
    
    Country co = lista.stream().filter(x -> x.getId()==id).findAny().get();
    if(id > lista.size()-1) throw new Exception("That id is not correct");
    return Response.ok(co).build();
    }catch(Exception e){
        
        return Response.status(404).entity(e.getMessage()).build();
        }
    }

I want to return a json when I don't have an Exception but when i have it I need to return a string with the exception message but this drop error of json parse.

A single quoted string is a valid JSON. So you could use:

return Response.status(404).entity("\"" + e.getMessage() + "\"").build();

However I advise you to return a JSON object instead. It gives you the flexibility to return extra metadata about the error.

You could use a Map<String, Object>:

Map<String, Object> errorDetails = new HashMap<>();
errorDetails.put("message", e.getMessage());
return Response.status(404).entity(errorDetails).build();

Or create a class for the error details:

public class ErrorDetails {

    private String message;

    ...
}

ErrorDetails errorDetails = new ErrorDetails;
errorDetails.setMessage(e.getMessage());
return Response.status(404).entity(errorDetails).build();

For reporting problems in an HTTP API, have a look at the RFC 7807.