原因是:maven的jar包管理问题
解决方法:
<dependency>
<groupId>org.elasticsearch</groupId>
<artifactId>elasticsearch</artifactId>
<version>xxx</version>
</dependency>
<dependency>
<groupId>org.elasticsearch.client</groupId>
<artifactId>transport</artifactId>
<version>xxx</version>
<exclusions>
<exclusion>
<groupId>org.elasticsearch.plugin</groupId>
<artifactId>transport-netty4-client</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.elasticsearch.plugin</groupId>
<artifactId>transport-netty4-client</artifactId>
<version>xxx</version>
</dependency>