@EnableRedisHttpSession
关注下这个注解，支持配置以下属性：
maxInactiveIntervalInSeconds:最大不活跃时间间隔，默认1800s。即超过这个时间间隔，session将会失效。
redisNamespace:redis命名空间，默认为空。多中心集成的时候,通过命名空间区分是否使用同一个session。
比如我这里设置的redisNamespace=iotcmp-cc，那么redis命名空间前缀即spring:session:iotcmp-cc
redisFlushMode:redis flush模式，支持两种模式：ON_SAVE和IMMEDIATE，默认ON_SAVE。

关于这两种模式的描述:
public enum RedisFlushMode {
    /**
     * Only writes to Redis when
     * {@link SessionRepository#save(org.springframework.session.Session)} is invoked. In
     * a web environment this is typically done as soon as the HTTP response is committed.
     */
    ON_SAVE,

    /**
     * Writes to Redis as soon as possible. For example
     * {@link SessionRepository#createSession()} will write the session to Redis. Another
     * example is that setting an attribute on the session will also write to Redis
     * immediately.
     */
    IMMEDIATE
}