public Object setSessionData(String key, Object value) {
        synchronized (sessionData) {
            return sessionData.put(key, value);
        }
    }
Saves given session data. Data are saved to temporary storage only and are accessible during
this session life only and only from this session instance.

@param key a <code>String</code> value of stored data key ID.
@param value a <code>Object</code> value of data stored in session.
@return the previous value associated with {@code key}, or
        {@code null} if there was no mapping for {@code key}.
        (A {@code null} return can also indicate that the map
        previously associated {@code null} with {@code key}.)
@see #getSessionData(String)
xmppserver/src/main/java/org/jivesoftware/openfire/session/LocalSession.java