Returns {@code true} if the associated session is valid (it exists and is not stopped nor expired),
{@code false} otherwise.
@param key the session key to use to look up the target session.
@return {@code true} if the session is valid (exists and is not stopped or expired), {@code false} otherwise.
Returns {@code true} if the associated session is valid (it exists and is not stopped nor expired), {@code false} otherwise.
@param key the session key to use to look up the target session. @return {@code true} if the session is valid (exists and is not stopped or expired), {@code false} otherwise.