问题描述：
Suppressed: org.elasticsearch.client.ResponseException: method [PUT], host [http://localhost:9200], URI [/search/doc/4?timeout=1m], status line [HTTP/1.1 400 Bad Request]
{"error":{"root_cause":[{"type":"invalid_type_name_exception","reason":"Document mapping type name can't start with '', found: [doc]"}],"type":"invalid_type_name_exception","reason":"Document mapping type name can't start with '', found: [_doc]"},"status":400}
at org.elasticsearch.client.RestClient.convertResponse(RestClient.java:283)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:261)
at org.elasticsearch.client.RestClient.performRequest(RestClient.java:235)
at org.elasticsearch.client.RestHighLevelClient.internalPerformRequest(RestHighLevelClient.java:1611)
... 5 more
问题原因：
旧版本ES必须指定type，新版java api默认type为_doc
解决方案：
- 指定type
IndexRequest indexRequest = new IndexRequest(INDEX, TYPE);
- 升级es至7.x以后版本