Get current logged in username in Spring Security

1. SecurityContextHolder + Authentication.getName()

import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
 
@Controller
public class LoginController {
 
  @RequestMapping(value="/login", method = RequestMethod.GET)
  public String printUser(ModelMap model) {
 
      Authentication auth = SecurityContextHolder.getContext().getAuthentication();
      String name = auth.getName(); //get logged in username
 
      model.addAttribute("username", name);
      return "hello";
 
  }
  //...

2. SecurityContextHolder + User.getUsername()

import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.User;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
 
@Controller
public class LoginController {
 
  @RequestMapping(value="/login", method = RequestMethod.GET)
  public String printUser(ModelMap model) {
 
      User user = (User)SecurityContextHolder.getContext().getAuthentication().getPrincipal();
      String name = user.getUsername(); //get logged in username
 
      model.addAttribute("username", name);
      return "hello";
 
  }
  

3. UsernamePasswordAuthenticationToken

This is more elegant solution, in runtime, Spring will injects UsernamePasswordAuthenticationTokeninto the Principal interface.

import java.security.Principal;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
 
@Controller
public class LoginController {
 
  @RequestMapping(value="/login", method = RequestMethod.GET)
  public String printWelcome(ModelMap model, Principal principal ) {
 
      String name = principal.getName(); //get logged in username
      model.addAttribute("username", name);
      return "hello";
 
  }
  //...