private Map<Object, Object> getAttributesLazy() {
        Map<Object, Object> attributes = getAttributes();
        if (attributes == null) {
            attributes = new HashMap<Object, Object>();
            setAttributes(attributes);
        }
        return attributes;
    }
Determines if this session is expired.

@return true if the specified session has expired, false otherwise.
core/src/main/java/org/apache/shiro/session/mgt/SimpleSession.java