Может @PathVariable возвращать NULL, если он не найден?

Question

Можно ли сделать генеракодицетагкод для возврата NULL, если переменная пути не в URL-адреса?В противном случае мне нужно сделать два обработчика.Один для @PathVariable и другой для /simple, но оба делают то же самое только в том случае, если нет определенной игры, я выбираю первый из списка, однако, если есть определенный параметр игры, я использую его.

@RequestMapping(value = {"/simple", "/simple/{game}"}, method = RequestMethod.GET)
public ModelAndView gameHandler(@PathVariable("example") String example,
            HttpServletRequest request) {

.

И это то, что я получаю, когда пытаясь открыть страницу GeneracodicCode:

вызвано: java.lang.illegalstateException: не удалось найти @ dathvariable [пример] в @requestmapping

Answer 1

They cannot be optional, no. If you need that, you need two methods to handle them.

This reflects the nature of path variables - it doesn't really make sense for them to be null. REST-style URLs always need the full URL path. If you have an optional component, consider making it a request parameter instead (i.e. using @RequestParam). This is much better suited to optional arguments.

Answer 2

As others have already mentioned No you cannot expect them to be null when you have explicitly mentioned the path parameters. However you can do something like below as a workaround -

@RequestMapping(value = {"/simple", "/simple/{game}"}, method = RequestMethod.GET)
public ModelAndView gameHandler(@PathVariable Map<String, String> pathVariablesMap,
            HttpServletRequest request) {
    if (pathVariablesMap.containsKey("game")) {
        //corresponds to path "/simple/{game}"
    } else {
        //corresponds to path "/simple"
    }           
}

If you are using Spring 4.1 and Java 8 you can use java.util.Optional which is supported in @RequestParam, @PathVariable, @RequestHeader and @MatrixVariable in Spring MVC

@RequestMapping(value = {"/simple", "/simple/{game}"}, method = RequestMethod.GET)
public ModelAndView gameHandler(@PathVariable Optional<String> game,
            HttpServletRequest request) {
    if (game.isPresent()) {
        //game.get()
        //corresponds to path "/simple/{game}"
    } else {
        //corresponds to path "/simple"
    }           
}

Answer 3

You could always just do this:

@RequestMapping(value = "/simple", method = RequestMethod.GET)
public ModelAndView gameHandler(HttpServletRequest request) {
    gameHandler2(null, request)
}

@RequestMapping(value = "/simple/{game}", method = RequestMethod.GET)
public ModelAndView gameHandler2(@PathVariable("game") String game,
        HttpServletRequest request) {

Answer 4

@RequestMapping(value = {"/simple", "/simple/{game}"}, method = RequestMethod.GET)
public ModelAndView gameHandler(@PathVariable(value="example",required = false) final String example)

Try this approach, it worked for me.