Spring

@RequestMapping(value = "/home", method = RequestMethod.GET) public String home(Model model) {
        List<WarehouseItem> clients = clientService.getAllClients();

        ComboBoxProperties comboBoxProperties = new ComboBoxProperties();
        List<String> companies = new ArrayList<>();
        List<String[]> products = new ArrayList<>();

        for ( Map.Entry<String, String[]> set: comboBoxProperties.getKeyValuesParForCompaniesAndProducts()
                                                                 .entrySet() ) {
            companies.add(set.getKey());
            products.add(set.getValue());
        }

        model.addAttribute("myMap", comboBoxProperties.getKeyValuesParForCompaniesAndProducts());
        model.addAttribute("test", comboBoxProperties.getKeyValuesParForCompaniesAndProducts().keySet());
        model.addAttribute("companies", companies);
        model.addAttribute("products", products);
        model.addAttribute("warehouseItems", clients);
        model.addAttribute("warehouseItem", new WarehouseItem());
        return "home";
    }

    @RequestMapping(value = "/home", method = RequestMethod.POST)
    public ModelAndView somethingElse(@RequestBody String key, Model model) {
        ComboBoxProperties comboBoxProperties = new ComboBoxProperties();
        ArrayList<String> comp = new ArrayList<>(
                Arrays.asList(comboBoxProperties.getKeyValuesParForCompaniesAndProducts().get(key)));
        model.addAttribute("comp", comp);
        ModelAndView view = new ModelAndView();
        view.setViewName("home");

        return view;
    }