JSON parse error: Cannot deserialize instance of `java.lang.Long - spring-boot

Question

I am using Spring boot I try to create a new Student.
#RequestMapping(path="/student/create", method=RequestMethod.POST)<br>
public ResponseEntity<String> createStudent(#RequestBody Long nummer, String firstname, String lastname){<br>
service.createStudent(matrikelnummer, vorname, nachname);<br>
return new ResponseEntity<String>("gut gemacht", HttpStatus.OK);
Here my RequestBody with RESTCLIENT
{"nummer":15557,"firstname":"toti","lastname":"Innna"}
I have this Error:
{"timestamp":"2019-12-20T19:41:30.083+0000","status":400,"error":"Bad
Request","message":"JSON parse error: Cannot deserialize instance of
java.lang.Long out of START_OBJECT token; nested exception is
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot
deserialize instance of java.lang.Long out of START_OBJECT token\n
at [Source: (PushbackInputStream); line: 1, column:
1]","trace":"org.springframework.http.converter.HttpMessageNotReadableException:
JSON parse error: Cannot deserialize instance of java.lang.Long out
of START_OBJECT token; nested exception is
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot
deserialize instance of java.lang.Long out of START_OBJECT token\n
at [Source: (PushbackInputStream); line: 1, column: 1]\r\n\tat

Answer 1

In your example the mapper expects the body to present a Long object, but you pass it a Student object. This does not match, so it throws an exception.
It is not necessary to list all the fields of the students as separate method arguments, you can just pass a Student object as RequestBody argument.
The object mapper will then try to resolve a Student instance from the provided JSON.
Example:
#RequestMapping(path="/student/create", method=RequestMethod.POST)
public ResponseEntity<String> createStudent(#RequestBody Student student){
service.createStudent(student);
return new ResponseEntity<String>("gut gemacht", HttpStatus.OK);
}