How do I implement Serializable? For storing my data in Session

Question

Hi I have been trying to do session replication between my 2 tomcat clusters...and also I am maintain sticky session...I am currently having a problem that after adding tag in web.xml and running my application it gives an error like **java.lang.IllegalArgumentException: setAttribute: Non-serializable attribute** and when I referred the tomcat documentation for finding solution it was mentioned that All your session attributes must implement java.io.Serializable

...and I get doubt here all my session attributes must implement serializable means that all the objects I am storing in the session using setattribute must implement serializable interface...that mean if I am doing

public class MySession {
  String sessionObj1 = "Hello";
  HttpSession session = request.getSession();
  session.setAttribute("New-Session-1", sessionObj1);
}

Here sessionObj1 is a String Object and serializable likewise I should set only objects that implements serializable interface