Using Elasticsearch Java Sdk

Starting with an empty Gradle project, the dependencies for the ElasticSearch Java SDK were added to the build.gradle file:

    //build.gradle
    dependencies {
      implementation 'co.elastic.clients:elasticsearch-java:8.1.3'
      implementation 'com.fasterxml.jackson.core:jackson-databind:2.12.3'
      implementation 'jakarta.json:jakarta.json-api:2.0.1'
    }

Then, a record type for storing data is defined:

  record Book(String title, String author, int publishedYear) { }

Get a reference to the ElasticSearch client object, which will be used for making any requests:

  RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)).build();
  ElasticsearchTransport transport = new RestClientTransport(restClient, new JacksonJsonpMapper());
  ElasticsearchClient client = new ElasticsearchClient(transport);

Create the index if it does not already exist (use dynamic mappings for now).

  ExistsRequest existRequest = new ExistsRequest.Builder().index("book").build();
  BooleanResponse existsResponse = client.indices().exists(existRequest);

  if (existsResponse.value() == false) {
    CreateIndexRequest request = new CreateIndexRequest.Builder().index("book").build();
    CreateIndexResponse createIndexResponse = client.indices().create(request);
  }

Insert a Book object into ElasticSearch.

  Book bk1 = new Book("Who Moved My Cheese", "Spencer Johnson", 1998);

  IndexResponse createResponse = client.index(i -> i
          .index("book")
          .id(bk1.title())
          .document(bk1)
  );
  System.out.println("New ver: " + createResponse.version());

Fetch by ID

  GetResponse<Book> retrieveResponse = client.get(g -> g
                  .index("book")
                  .id(bk1.title()),
          Book.class
  );

  if (retrieveResponse.found()) {
    Book bk2 = retrieveResponse.source();
    System.out.println("Author: " + bk2.author());
  } else {
    System.out.println("Book not found");
  }

Simple fieldName=value Search query

  SearchResponse<Book> response = client.search(s -> s
                  .index("book")
                  .query(q -> q
                          .match(t -> t
                                  .field("author")
                                  .query(bk1.author())
                          )
                  ),
          Book.class
  );

  TotalHits total = response.hits().total();
  boolean isExactResult = total.relation() == TotalHitsRelation.Eq;

  if (isExactResult) {
    System.out.println("There are " + total.value() + " results");
  } else {
    System.out.println("There are more than " + total.value() + " results");
  }

  List<Hit<Book>> hits = response.hits().hits();
  for (Hit<Book> hit: hits) {
    Book bk3 = hit.source();
    System.out.println("Found book " + bk3.title() + ", score " + hit.score());
  }

Drop the index

  DeleteIndexRequest delReq = new DeleteIndexRequest.Builder().index(List.of("book")).build();
  DeleteIndexResponse delResp = client.indices().delete(delReq);

Close the REST client object

  restClient.close();