Spring MVC REST not null constraint does not work on missing request param - rest

Question

Not null validation does not work for a case:
#RestController
public class BookController {
#GetMapping("/api/books/search")
public Page<Book> get(#RequestParam(name = "bookId") #Valid #NotNull Long bookId, Pageable pageable) {
.... // #1
}
}
If I call GET http://localhost:8080/api/books/search?bookId=
bookId is null on row #1. It's strange behaviour, cause if I do not provide bookId it fails.
#NotNull validation is not triggered.

Answer 1

#NotNull validation is not triggered.
When you want the validation to be triggered, the controller class must be annotated with #Validated:
#Validated
#RestController
public class BookController {
...
}
Quoting the documentation:
To be eligible for Spring-driven method validation, all target classes need to be annotated with Spring’s #Validated annotation.
The #RequestParam annotation has a required element where the default value is true. It simply indicates that the parameter itself must be present in the URL (either ?id or ?id=), but it doesn't require a non-null value for that parameter. If you need to validate the value of such parameter, then you should use Bean Validation annotations.
Consider, for instance, the following controller method:
#GetMapping("/foo")
public ResponseEntity<Foo> get(#RequestParam("id") Long id) {
...
}
The following request will result in a response with the 400 status code because the id parameter is not present:
GET /foo HTTP/1.1
Host: example.org
On the other hand, the following request is considered to be valid because the id parameter is present (even though there's no value associated with it):
GET /foo?id HTTP/1.1
Host: example.org
To refuse null values, use the #NotNull annotation (and ensure that controller class is annotated with #Validated):
#GetMapping("/foo")
public ResponseEntity<Foo> get(#RequestParam("id") #NotNull Long id) {
...
}

Answer 2

There are different concepts. Method parameters annotated with #RequestParam are by default required. You can set #RequestParam(required = false) to disable this.
Your parameter however is of type Long (object). You can not give it and then by default it will be null (since you did not set a default - like #RequestParam(defaultValue = )).
Best way is to either set a default value or to check for null in your method.