查看源代码得知zookeeper（版本3.4.13）内部的日志用的slf4j，项目启动zk连接了之后一直在打debug日志（如下所示），甚是讨厌，logback日志级别调成info没用。
17:24:53.707 [main-SendThread(DESKTOP-L0MISLK:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x1003d58f1cd0011 after 1ms 17:24:55.042 [main-SendThread(DESKTOP-L0MISLK:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x1003d58f1cd0011 after 1ms 17:24:56.376 [main-SendThread(DESKTOP-L0MISLK:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x1003d58f1cd0011 after 1ms 17:24:57.711 [main-SendThread(DESKTOP-L0MISLK:2181)] DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid: 0x1003d58f1cd0011 after 1ms
原因：
在a项目里用的zk连接，而logback.xml是放在a项目的父项目b里的，在a项目自己src/main/resources里放了logback.xml（调成info级别）后，问题解决。