As we all know elasticsearch has indexes, that you can query to get data. That is simple with spring data configured or rest template. So, I came across a complex query I need to perform. So let see.
The Query I was to do on two user indexes on different types, having some similar data. So I did some r&d and got to know about multi-search queries.
Multi-search queries enable us to query two or more indexes, with queries for each index. Check out at the link below
https://www.elastic.co/guide/en/elasticsearch/client/java-rest/master/java-rest-high-multi-search.html

My Solution

The solution multi-search API provided was good, but complex for my case, as I had different indexes but with the same fields in both like userId, id, name.
So I do use multi indexes but with a single search and single query. Let see.

Steps

1.Create a method and initialize High-Level Rest Client(You can use directly in your main method too, I just prefer keeping separate code)

 private RestHighLevelClient restHighLevelClient() {
        log.debug("RestHighLevelClient initialization");
        String esHost = // host of elasticsearch
        Integer esPort = // port of elasticsearch
        return new RestHighLevelClient(RestClient.builder(new HttpHost(esHost, esPort)));
    }

2.Search method with a query

search(keyword: string) {
// Create a Bool query 
BoolQueryBuilder boolQuery = QueryBuilders.boolQuery();
boolQuery.must(query);
// Create a search request 
// pass your indexes in place of indexA, indexB
SearchRequest searchRequest = new SearchRequest("indexA", "indexB");
// CReate a search Source
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
 searchSourceBuilder.query(boolQuery);
 searchRequest.source(searchSourceBuilder);
// Create object to get Response
SearchResponse searchResponse = restHighLevelClient().search(searchRequest, RequestOptions.DEFAULT);
// Parsing response 
SearchHit[] searchHits = searchResponse.getHits().getHits();
}

3.Parsing data from Search hit by looping
Just pass the fields and cast data type to get the expected response

for(SearchHit hit: searchHits) {
   Map<String, Object> sourceAsMap = hit.getSourceAsMap();
   String field = (String) sourceAsMap.get("fieldName");
   Integer field2 = (Integer) sourceAsMap.get("fieldName");
}

4.This is how you can do the multi-search. Just replace your query, indexes as required, and parse data

Note: You must be thinking about why we did not use any DTO instead. This is because, we require just 3 fields for now, which can be handled easily. We using JSONObject for this. You can create any class or DTO for parsing.

I hope it will help you, thanks for reading.

Also, checkout Tekraze.com for more articles.