How to provide highlighting with Spring data elasticsearch

Question

it seems that SpringData ES don\'t provide classes to fetch highlights returned by ES. Spring Data can return Lists of Objects but the highlights sections in the Json return

Answer 1

Actually, you could do the following, with a custom ResultExtractor:

QueryBuilder query = QueryBuilders.matchQuery("name", "tom"); 
SearchQuery searchQuery = new NativeSearchQueryBuilder()
                           .withQuery(query)
                           .withHighlightFields(new Field("name")).build();
return elasticsearchTemplate.query(searchQuery.build(), new CustomResultExtractor());

And then

public class CustomResultExtractor implements ResultsExtractor> {

private final DefaultEntityMapper defaultEntityMapper;

public CustomResultExtractor() {
    defaultEntityMapper = new DefaultEntityMapper();
}


@Override
public List extract(SearchResponse response) {
    return StreamSupport.stream(response.getHits().spliterator(), false) 
        .map(this::searchHitToMyClass) 
        .collect(Collectors.toList());
}

private MyClass searchHitToMyClass(SearchHit searchHit) {
    MyElasticSearchObject myObject;
    try {
        myObject = defaultEntityMapper.mapToObject(searchHit.getSourceAsString(), MyElasticSearchObject.class);
    } catch (IOException e) {
        throw new ElasticsearchException("failed to map source [ " + searchHit.getSourceAsString() + "] to class " + MyElasticSearchObject.class.getSimpleName(), e);
    }
    List highlights = searchHit.getHighlightFields().values()
        .stream() 
        .flatMap(highlightField -> Arrays.stream(highlightField.fragments())) 
        .map(Text::string) 
        .collect(Collectors.toList());
    // Or whatever you want to do with the highlights
    return new MyClass(myObject, highlights);
}}

Note that I used a list but you could use any other iterable data structure. Also, you could do something else with the highlights. Here I'm simply listing them.