An abstract {@code SessionDAO} implementation that performs some sanity checks on session creation and reading and allows for pluggable Session ID generation strategies if desired. The {@code SessionDAO} {@link SessionDAO#update update} and {@link SessionDAO#remove remove} methods are left to subclasses. <h3>Session ID Generation</h3> This class also allows for plugging in a {@link SessionIdGenerator} for custom ID generation strategies. This is optional, as the default generator is probably sufficient for most cases. Subclass implementations that do use a generator (default or custom) will want to call the {@link #generateSessionId(hunt.shiro.session.Session)} method from within their {@link #doCreate} implementations. <p/> Subclass implementations that rely on the EIS data store to generate the ID automatically (e.g. when the session ID is also an auto-generated primary key), they can simply ignore the {@code SessionIdGenerator} concept entirely and just return the data store's ID from the {@link #doCreate} implementation.