Null check for a single id parameter on the Controller method

In a Spring Boot Controller, I am trying to validate an id field in Long type as shown below:

@GetMapping("/{id}")
public ResponseEntity<EmployeeResponse> getById(@PathVariable @NotNull Long id) {
    final EmployeeResponse response = employeeService.getById(id);
    return ResponseEntity.ok(...);
}

But when I try to send request with null id parameter, ı get the following error:

> "Failed to convert value of type 'java.lang.String' to required type 'java.lang.Long'; For input string: ":id""

I also tried using long and @Valid annotation, but does not make any sense and a similar error is encountered. So, is it possible to validate id parameter of the request?

Not sure if it make sense to have @PathVariable as @NotNull?
Because it's different url if it's null. So you could handle that with other endpoint @GetMapping("/")

Another approach, which I pretty much always use for path & normal params in the URL, is the following: Just use String for every parameter.

As URL is easily manipulable by any user, they can e.g. just enter ".../sos" instead of a valid number and you'll receive the same error.

Why? Everything in a URL is a String. When Spring Boot notices the controller accepting a Long as a parameter, it tries to parse it by itself.

This won't happen if you use a String, as previously mentioned: everything in the URL already is a String and SB won't need to parse it to any other datatype.

I'd recommend you to just have String parameters in your method aswell and then just do the parsing/converting manually via .getById(Long.parseLong(id));.

This way you can e.g. catch any parse exception and return an appropriate error message.

You need to add values to @GetMapping, because URL will wait path with data, cuz data also means path. Also you need to add @PathVariable(required = false), it means your address in mapping will not wait data, and can come null if you ust call "/", in your service you see null data for id, cuz calls another value for your path.

@GetMapping(value = {"/{id}", ""})
public ResponseEntity<EmployeeResponse> getById(@PathVariable(required = false) Long id) {
    if (id == null) { // Do something when null
        }
        else {// do another thing
        }
        return "your data";
    }

If you are using

@PathVariable(...)

They cannot be optional. 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 use

@RequestParam(...)

instead.

You can use
@NotNull
in your entities itself.

I suggest you check this
especially sixth paragraph, where he explains which sort of constraints work for which datatypes.