Get UserDetails object from Security Context in Spring MVC controller

I'm using Spring Security 3 and Spring MVC 3.05.

I would like to print username of currently logged in user,how can I fetch UserDetails in my Controller?

@RequestMapping(value="/index.html", method=RequestMethod.GET)
	public ModelAndView indexView(){
         UserDetails user = ?
                mv.addObject("username", user.getUsername());
		ModelAndView mv = new ModelAndView("index");
		return mv;
	}	

If you already know for sure that the user is logged in (in your example if /index.html is protected):

UserDetails userDetails =
 (UserDetails)SecurityContextHolder.getContext().getAuthentication().getPrincipal();

To first check if the user is logged in, check that the current Authentication is not a AnonymousAuthenticationToken.

Authentication auth = SecurityContextHolder.getContext().getAuthentication();
if (!(auth instanceof AnonymousAuthenticationToken)) {
        // userDetails = auth.getPrincipal()
}

Let Spring 3 injection take care of this.

Thanks to tsunade21 the easiest way is:

 @RequestMapping(method = RequestMethod.GET)   
 public ModelAndView anyMethodNameGoesHere(Principal principal) {
        final String loggedInUserName = principal.getName();

 }

If you just want to print user name on the pages, maybe you'll like this solution. It's free from object castings and works without Spring Security too:

@RequestMapping(value = "/index.html", method = RequestMethod.GET)
public ModelAndView indexView(HttpServletRequest request) {

	ModelAndView mv = new ModelAndView("index");

	String userName = "not logged in"; // Any default user  name
	Principal principal = request.getUserPrincipal();
	if (principal != null) {
		userName = principal.getName();
	}

	mv.addObject("username", userName);

    // By adding a little code (same way) you can check if user has any
    // roles you need, for example:

    boolean fAdmin = request.isUserInRole("ROLE_ADMIN");
    mv.addObject("isAdmin", fAdmin);

	return mv;
}

Note "HttpServletRequest request" parameter added.

Works fine because Spring injects it's own objects (wrappers) for HttpServletRequest, Principal etc., so you can use standard java methods to retrieve user information.

if you are using spring security then you can get the current logged in user by

Authentication auth = SecurityContextHolder.getContext().getAuthentication();
     String name = auth.getName(); //get logged in username

That's another solution (Spring Security 3):

public String getLoggedUser() throws Exception {
    String name = SecurityContextHolder.getContext().getAuthentication().getName();
    return (!name.equals("anonymousUser")) ? name : null;
}

You can use below code to find out principal (user email who logged in)

  org.opensaml.saml2.core.impl.NameIDImpl principal =  
  (NameIDImpl) SecurityContextHolder.getContext().getAuthentication().getPrincipal();

  String email = principal.getValue();

This code is written on top of SAML.