项目使用dubbo 、zookeeper服务报 Could not initialize class org.I0Itec.zkclient.ZkClient

项目中使用了dubbo 服务，用zookeeper 做注册中心，用的logback 作为日志框架，在启动项目时候报错如下：

Caused by: java.lang.NoClassDefFoundError: Could not initialize class org.I0Itec.zkclient.ZkClient
at com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperClient.<init>(ZkclientZookeeperClient.java:25) ~[dubbo-2.5.3.jar:2.5.3]
at com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperTransporter.connect(ZkclientZookeeperTransporter.java:10) ~[dubbo-2.5.3.jar:2.5.3]
at com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter$Adpative.connect(ZookeeperTransporter$Adpative.java) ~[na:2.5.3]
at com.alibaba.dubbo.registry.zookeeper.ZookeeperRegistry.<init>(ZookeeperRegistry.java:71) ~[dubbo-2.5.3.jar:2.5.3]

看第一句 Caused by: java.lang.NoClassDefFoundError: Could not initialize class org.I0Itec.zkclient.ZkClient

这句说是不能找到初始化ZKClient 类，查了网上资源，说是缺少 jar包，看项目pom， 确实引入了该jar

<dependency>
<groupId>com.101tec</groupId>
<artifactId>zkclient</artifactId>
<version>0.3</version>
</dependency>

再网上翻启动日志, 看到一行

java.lang.NoClassDefFoundError: org/apache/log4j/Logger
at org.I0Itec.zkclient.ZkClient.<clinit>(ZkClient.java:57) ~[zkclient-0.3.jar:0.3]
at com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperClient.<init>(ZkclientZookeeperClient.java:25) ~[dubbo-2.5.3.jar:2.5.3]
at com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperTransporter.connect(ZkclientZookeeperTransporter.java:10) ~[dubbo-2.5.3.jar:2.5.3]
at com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter$Adpative.connect(ZookeeperTransporter$Adpative.java) ~[na:2.5.3]

说是缺少log4j 包，这么说dubbo内部使用的log4j, 而我在我最后pom里加入了排除log4j

<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
<exclusion>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
</exclusion>
</exclusions>

估计就是这个问题，然后 删除 log4j 排除 ，再重启，成功。