How to get the username (email in my case) in Spring Security [UserDetails/String] - spring

Question

I would like to get the e-mail which is username in my application to set the user which send a message. I decided to use typical method i.e. principal and getUsername():
#PostMapping("/messages/{id}")
#ResponseStatus(HttpStatus.CREATED)
public MessageDTO addOneMessage(#RequestBody MessageRequest messageRequest, #PathVariable ("id") Long id) {
checkIfChannelExists(id);
String content = messageRequest.getContent();
Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();
String username = ((UserDetails) principal).getUsername();
Employee author = employeeRepository.findByEmail(username).get();
Message message = new Message(content, author, id);
messageRepository.save(message);
return new MessageDTO(message);
}
And MessageRequest.java:
#Data
#NoArgsConstructor
#AllArgsConstructor
public class MessageRequest {
#NonNull
private String content;
}
But, in this way I still get:
"message": "java.lang.String cannot be cast to org.springframework.security.core.userdetails.UserDetails"
What is wrong in my implementation? To be more precise, I use Postman to test POST requests:
{
"content": "something"
}

Answer 1

If you only need to retrieve the username you can get it through Authentication ie.
Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
String username = authentication.getName();
instead of typecasting to your class springcontext provide the almost all details about the user.
If you want the controller to get the user name to test.
please use this code.
//using authentication
#RequestMapping(value = "/name", method = RequestMethod.GET)
#ResponseBody
public String currentUserName(Authentication authentication) {
return authentication.name();
}
//using principal
#RequestMapping(value = "/name", method = RequestMethod.GET)
#ResponseBody
public String currentUserName(Principal principal) {
return principal.getName();
}