public void setStopTimestamp(Date stopTimestamp) {
        this.stopTimestamp = stopTimestamp;
    }
Returns the time the session was stopped, or <tt>null</tt> if the session is still active.
<p/>
A session may become stopped under a number of conditions:
<ul>
<li>If the user logs out of the system, their current session is terminated (released).</li>
<li>If the session expires</li>
<li>The application explicitly calls {@link #stop()}</li>
<li>If there is an internal system error and the session state can no longer accurately
reflect the user's behavior, such in the case of a system crash</li>
</ul>
<p/>
Once stopped, a session may no longer be used.  It is locked from all further activity.

@return The time the session was stopped, or <tt>null</tt> if the session is still
active.
core/src/main/java/org/apache/shiro/session/mgt/SimpleSession.java