@PostMapping("/register")
public String postRegister(Users users, HttpServletRequest request) {
    String password=users.getPassword();
    /*System.out.println("STring password "+password);
    System.out.println("user.getpassword "+users.getPassword());*/
/*  Users dbUser=userService.save(users);
    if(dbUser!=null) {*/
        userService.save(users);
        securityService.autologin(users.getEmail(),password,request);
        if(users.getRole().equalsIgnoreCase("USER")) {
            return "redirect:/users/dashboard";

    }

    return "redirect:/register";
}

@Override
public void autologin(String email, String password, HttpServletRequest request) {
    UserDetails userDetails=userDetailsService.loadUserByUsername(email);
    Authentication authentication=authenticationManager.authenticate(new UsernamePasswordAuthenticationToken(email, password,userDetails.getAuthorities()));
    SecurityContextHolder.getContext().setAuthentication(authentication);
    request.getSession().setAttribute(HttpSessionSecurityContextRepository.SPRING_SECURITY_CONTEXT_KEY, SecurityContextHolder.getContext());
}

<form method="post" th:action="@{/register}" th:object="${user}">
  <div class="container">
    <h1>Register</h1>
    <p>Please fill in this form to create an account.</p>
    <hr>
    <label for="name"><b>Name</b></label>
    <input type="text" placeholder="Enter name" name="name" th:field="*{name}" required>

    <label for="email"><b>Email</b></label>
    <input type="email" placeholder="Enter Email" name="email" th:field="*{email}" required>

    <label for="mobile"><b>Mobile</b></label>
    <input type="text" placeholder="Enter mobile" name="mobile" th:field="*{mobile}" required>

    <label for="password"><b>Password</b></label>
    <input type="password" placeholder="Enter password" name="password" th:field="*{password}" required>

    <hr>
    <p>By creating an account you agree to our <a href="#">Terms & Privacy</a>.</p>

    <button type="submit" class="registerbtn">Register</button>
  </div>

  <div class="container signin">
    <p>Already have an account? <a href="#">Sign in</a>.</p>
  </div>
</form>