Getting syntax error for Spring security with Jersey Rest API

I am doing authentication for REST Services.

So If user is unauthenticated then I want to send the user as "unauthenticated user" as repsonse in JSON format.

below is my code . I have set the content type as APPLICATION_JSON then I am getting the response as syntax error on postman tool. I can see the exact error in plainText or in Xml but not able to see the response in JSON.

Could anybody help me to get out from this issu please.

@Override

public void commence(HttpServletRequest request, HttpServletResponse response,

      AuthenticationException authException) throws IOException {



        response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);

        response.setHeader("Connection", "keep-alive");

        response.setContentType(MediaType.APPLICATION_JSON);

        String msg = authException.getMessage(); 

        response.getOutputStream().println("{ \"error\": \"" + msg+ "\" }");

      }

}