Spring MVC: how to indicate whether a path variable is required or not?

问题

I am doing a Spring web. For a controller method, I am able to use RequestParam to indicate whether a parameter it is required or not. For example:

@RequestMapping({"customer"}) 
public String surveys(HttpServletRequest request, 
@RequestParam(value="id", required = false) Long id,            
Map<String, Object> map)

I would like to use PathVariable such as the following:

@RequestMapping({"customer/{id}"}) 
public String surveys(HttpServletRequest request, 
@PathVariable("id") Long id,            
Map<String, Object> map)

How can I indicate whether a path variable is required or not? I need to make it optional because when creating a new object, there is no associated ID available until it is saved.

Thanks for help!

回答1:

There's no way to make it optional, but you can create two methods with one having the @RequestMapping({"customer"}) annotation and the other having @RequestMapping({"customer/{id}"}) and then act accordingly in each.

回答2:

VTTom`s solution is right, just change "value" variable to array and list all url possibilities: value={"/", "/{id}"}

@RequestMapping(method=GET, value={"/", "/{id}"})
public void get(@PathVariable Optional<Integer> id) {
  if (id.isPresent()) {
    id.get()   //returns the id
  }
}

回答3:

I know this is an old question, but searching for "optional path variable" puts this answer high so i thought it would be worth pointing out that since Spring 4.1 using Java 1.8 this is possible using the java.util.Optional class.

an example would be (note the value must list all the potential routes that needs to match, ie. with the id path variable and without. Props to @martin-cmarko for pointing that out)

@RequestMapping(method=GET, value={"/", "/{id}"})
public void get(@PathVariable Optional<Integer> id) {
  if (id.isPresent()) {
    id.get()   //returns the id
  }
}

回答4:

VTToms answer will not work as without id in path it will not be matched (i.e will not find corresponding HandlerMapping) and consequently controller will not be hit. Rather you can do -

@RequestMapping({"customer/{id}","customer"}) 
public String surveys(HttpServletRequest request, @PathVariable Map<String, String> pathVariablesMap, Map<String, Object> map) {
    if (pathVariablesMap.containsKey("id")) {
        //corresponds to path "customer/{id}"
    }
    else {
        //corresponds to path "customer"
    }
}

You can also use java.util.Optional which others have mentioned but it requires requires Spring 4.1+ and Java 1.8..

回答5:

There is a problem with using 'Optional'(@PathVariable Optional id) or Map (@PathVariable Map pathVariables) in that if you then try to create a HATEOAS link by calling the controller method it will fail because Spring-hateoas seems to be pre java8 and has no support for 'Optional'. It also fails to call any method with @PathVariable Map annotation.

Here is an example that demonstrates the failure of Map

   @RequestMapping(value={"/subs","/masterclient/{masterclient}/subs"}, method = RequestMethod.GET)
   public List<Jobs>  getJobListTest(
         @PathVariable  Map<String, String> pathVariables,
         @RequestParam(value="count", required = false, defaultValue = defaultCount) int count) 
   {

      if (pathVariables.containsKey("masterclient")) 
      {
         System.out.println("Master Client = " + pathVariables.get("masterclient"));
      } 
      else 
      {
         System.out.println("No Master Client");
      }




  //Add a Link to the self here.
  List list = new ArrayList<Jobs>();
  list.add(linkTo(methodOn(ControllerJobs.class).getJobListTest(pathVariables, count)).withSelfRel());

  return list;

}

来源：https://stackoverflow.com/questions/17821731/spring-mvc-how-to-indicate-whether-a-path-variable-is-required-or-not

标签

Spring

spring-mvc

path-variables