Return.map lambda 和抛出异常的 function

Question

Is there any way to use mapping optional entity as shown below when the function called in lambda throws an exception and when it does I want to pass this exception to function that called getFieldHives in first place, IDE force me to wrap it in try/catch block and when trying to throw it again i end up with loop of try/catch. Or perhaps there is other way of approaching this issue, my main goal is to avoid using optionalFieldDAO.isPresent() and optionalFieldDAO.get().

public List<HiveResponse> getFieldHives(String token, Long id) throws UserNotFoundException, FieldNotFoundException {
Optional<FieldDAO> optionalFieldDAO = fieldRepository.findById(id);

        return optionalFieldDAO
                .map(fieldDAO -> createFieldHivesResponse(fieldDAO, user))
                .orElseThrow(() -> new FieldNotFoundException("Field not found!"));
}

private List<HiveResponse> createFieldHivesResponse(FieldDAO fieldDAO, UserDAO user) throws FieldNotOwnedException {
        if(!user.getFieldDAOList().contains(fieldDAO)) throw new FieldNotOwnedException("Field not owned!");
        
        //rest of code
    }

Answer 1

Optional field can contain empty value(in case of null) or value. but your method return type is list. so you need to collect values in a list

    public List<HiveResponse> getFieldHives(String token, Long id) throws UserNotFoundException, FieldNotFoundException {
Optional<FieldDAO> optionalFieldDAO = fieldRepository.findById(id);
        List<HiveResponse> hiveResponses = new ArrayList<>();
        optionalFieldDAO.ifPresent(dao-> {
            hiveResponses.addAll(createFieldHivesResponse(dao,user));
        });
        return hiveResponses;
}

private List<HiveResponse> createFieldHivesResponse(FieldDAO fieldDAO, UserDAO user) throws FieldNotOwnedException {
        if(!user.getFieldDAOList().contains(fieldDAO)) throw new FieldNotOwnedException("Field not owned!");
        
        //rest of code
    }