//backend.
@PostMapping("/")
public List<A> addList(@RequestBody A aObject){
//......ur code
}
class A{
int num;
String name;
List<B> bList;
//getters and setters and default constructor
}
class B{
int d;
//defalut Constructor & gettes&setters
}
// postman
{
"num":value,
"name":value,
"bList":[{
"key":"value",
"key":"value",.....
}]
}