9200 端口

9200 是 HTTP 协议的 RESTful 接口。

9300 端口

9300 是 TCP 通讯端口，集群间和 TCP Client 都走的它。

What are ports 9200 and 9300 used for?

9200 is for REST.

9300 for nodes communication.

参考 

What are ports 9200 and 9300 used for?

https://discuss.elastic.co/t/what-are-ports-9200-and-9300-used-for/238578

Java Transport Client

https://www.elastic.co/guide/en/elasticsearch/client/java-api/current/client.html