java.io.NotSerializableException when implementing UserDetailsService - spring

Question

I am working with spring-security-oauth2 and I faced with such exception:
Caused by: java.io.NotSerializableException: com.samsung.diary.security.UserDetailsServiceImpl
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
In my config file i have:
<beans:bean id="clientDetailsUserService" class="org.springframework.security.oauth2.provider.client.ClientDetailsUserDetailsService">
<beans:constructor-arg ref="clientDetails" />
</beans:bean>
<authentication-manager id="clientAuthenticationManager" >
<authentication-provider user-service-ref="clientDetailsUserService" />
</authentication-manager>
<authentication-manager alias="authenticationManager">
<authentication-provider user-service-ref="userDetailsService">
</authentication-provider>
</authentication-manager>
If I change it to:
<beans:bean id="clientDetailsUserService" class="org.springframework.security.oauth2.provider.client.ClientDetailsUserDetailsService">
<beans:constructor-arg ref="clientDetails" />
</beans:bean>
<authentication-manager id="clientAuthenticationManager" >
<authentication-provider user-service-ref="clientDetailsUserService" />
</authentication-manager>
<authentication-manager alias="authenticationManager">
<authentication-provider>
<user-service>
<user name="2" password="2" authorities="ROLE_USER" />
</user-service>
</authentication-provider>
</authentication-manager>
everething works perfect.
My UserDetailsService implementation:
public class UserDetailsServiceImpl implements UserDetailsService {
#Autowired
#Qualifier("usersDAO")
private UsersDAO dao;
#Transactional(readOnly = true)
public UserDetails loadUserByUsername(String username)
throws UsernameNotFoundException, DataAccessException {
final com.samsung.diary.domain.User userEntity = dao.findByLogin(username);
if (userEntity == null)
throw new UsernameNotFoundException("user not found");
String login = userEntity.getLogin();
String password = userEntity.getPassword();
boolean enabled = userEntity.getEnabled().equals("true");
boolean accountNonExpired = enabled;
boolean credentialsNonExpired = enabled;
boolean accountNonLocked = enabled;
GrantedAuthority auth = new GrantedAuthority() {
private static final long serialVersionUID = 1L;
public String getAuthority() {
return userEntity.getAuthority();
}
};
Set<GrantedAuthority> set = new HashSet<GrantedAuthority>();
set.add(auth);
UserDetails details = new User(login, password, enabled, accountNonExpired, credentialsNonExpired, accountNonLocked,
set);
return details;
}
}
As I understand there is something connected with Serializable interface but I can't figure out how to solve it.
EDIT: I made UserDetailsServiceImpl and UsersDAO Serializable and now it works. But I still don't understand where my UserDetailsServiceImpl is being written in a stream.
If someone give me a hint I would be very appreciated.