ES Cluster via proxy IP, but listener timeout after waiting for [30000] ms

Elastic Stack Elasticsearch
6

Means that if we use Java rest client to search es result, like:

SearchRequest searchRequest = new SearchRequest(); 
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); 
searchSourceBuilder.query(QueryBuilders.matchAllQuery());

If request with curl -XGET which java rest client used? Thanks.