How to handle value in controller from dropdown list?

Question

Java

Hello, on the html page I get the value from the list (plant id)

<form th:action="@{'/plantAdd/'+${boxId}}" method='POST'>
    <table>
        <tr>
            <td>Select plant :</td>
            <td>
                <select name="neededId">
                    <option value=""> -- </option>
                    <option th:each="plant : ${plants}"
                            th:value="${plant.id}"
                            th:utext="${plant.name}">
                    </option>
                </select>

            </td>
        </tr>

        <tr>
            <td><input name="submit" type="submit" value="submit" /></td>
        </tr>
    </table>
</form>

further on this id, I will search in the controller (implement any logic there) there is now a lot left from my previous attempts to get the id
, how can I get it in these controllers?

@RequestMapping(value = "/plantAdd/{boxId}", method = RequestMethod.GET)
    public String plantAdd(Model model,
                           @PathVariable(name = "boxId") Long boxId){

        List<MyPlantNamesExp> listPlantNames = myPlantNameExpDAO.getNames();
        MyPlantNamesExp test = listPlantNames.get(0);
        logger.info("Add method : " + test.toString());

        model.addAttribute("ddForm", new DropDownForm());

        model.addAttribute("plants", listPlantNames);

        return "addPlant";
    }

    @RequestMapping(value = "/plantAdd/{boxId}", method = RequestMethod.POST)
    public String plantAdd(Model model, DropDownForm ddForm,
                           @PathVariable(name = "boxId") Long boxId) throws ResourceNotFoundException {
      //  logger.info("from user action : " + Long.parseLong(ddForm.getPlantName(), 10));
        logger.info("value from request");
        Plant plant = new Plant();
        Long id = Long.parseLong(ddForm.getPlantName(), 10);

        plant.setResponsibleGrowBox(growBoxService.findById(boxId));
        plant.setMyPlantId(myPlantService.findById(id).getId());

        return "addPlant";
    }

Answer 1

Hello!
I will write an example code, you already adapt it for yourself.
In the dropdown controller, you can get both the object itself and the object id, and then find this object in the database by ID.
Object lookup by ID option:
You can use Optional to avoid NPE.Optional<Plant>