Can @PathVariable return null if it's not found?

问题

Is it possible to make the @PathVariable to return null if the path variable is not in the url? Otherwise I need to make two handlers. One for /simple and another for /simple/{game}, but both do the same just if there is no game defined i pick first one from a list however if there is a game param defined then i use it.

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

And this is what I get when trying to open page /simple:

Caused by: java.lang.IllegalStateException: Could not find @PathVariable [example] in @RequestMapping

回答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.

回答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"
    }           
}

回答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) {

回答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.

来源：https://stackoverflow.com/questions/5493767/can-pathvariable-return-null-if-its-not-found

标签

java

spring-3

spring-annotations

path-variables