Search API

Let’s first look at some of the optional arguments of a SearchRequest:

SearchRequest searchRequest = new SearchRequest("posts"); 
searchRequest.types("doc"); 

There are a couple of other interesting optional parameters:

searchRequest.routing("routing"); 

searchRequest.indicesOptions(IndicesOptions.lenientExpandOpen()); 

searchRequest.preference("_local"); 

Most options controlling the search behavior can be set on the SearchSourceBuilder, which contains more or less the equivalent of the options in the search request body of the Rest API.

Here are a few examples of some common options:

SearchSourceBuilder sourceBuilder = new SearchSourceBuilder(); 
sourceBuilder.query(QueryBuilders.termQuery("user", "kimchy")); 
sourceBuilder.from(0); 
sourceBuilder.size(5); 
sourceBuilder.timeout(new TimeValue(60, TimeUnit.SECONDS)); 

After this, the SearchSourceBuilder only needs to be added to the SearchRequest:

SearchRequest searchRequest = new SearchRequest();
searchRequest.source(sourceBuilder);

Search queries are created using QueryBuilder objects. A QueryBuilder exists for every search query type supported by Elasticsearch’s Query DSL.

A QueryBuilder can be created using its constructor:

MatchQueryBuilder matchQueryBuilder = new MatchQueryBuilder("user", "kimchy"); 

Once created, the QueryBuilder object provides methods to configure the options of the search query it creates:

matchQueryBuilder.fuzziness(Fuzziness.AUTO); 
matchQueryBuilder.prefixLength(3); 
matchQueryBuilder.maxExpansions(10); 

QueryBuilder objects can also be created using the QueryBuilders utility class. This class provides helper methods that can be used to create QueryBuilder objects using a fluent programming style:

QueryBuilder matchQueryBuilder = QueryBuilders.matchQuery("user", "kimchy")
                                                .fuzziness(Fuzziness.AUTO)
                                                .prefixLength(3)
                                                .maxExpansions(10);

Whatever the method used to create it, the QueryBuilder object must be added to the SearchSourceBuilder as follows:

searchSourceBuilder.query(matchQueryBuilder);

The Building Queries page gives a list of all available search queries with their corresponding QueryBuilder objects and QueryBuilders helper methods.

The SearchSourceBuilder allows to add one or more SortBuilder instances. There are four special implementations (Field-, Score-, GeoDistance- and ScriptSortBuilder).

sourceBuilder.sort(new ScoreSortBuilder().order(SortOrder.DESC)); 
sourceBuilder.sort(new FieldSortBuilder("_uid").order(SortOrder.ASC));  

By default, search requests return the contents of the document _source but like in the Rest API you can overwrite this behavior. For example, you can turn off _source retrieval completely:

sourceBuilder.fetchSource(false);

The method also accepts an array of one or more wildcard patterns to control which fields get included or excluded in a more fine grained way:

String[] includeFields = new String[] {"title", "user", "innerObject.*"};
String[] excludeFields = new String[] {"_type"};
sourceBuilder.fetchSource(includeFields, excludeFields);

Highlighting search results can be achieved by setting a HighlightBuilder on the SearchSourceBuilder. Different highlighting behaviour can be defined for each fields by adding one or more HighlightBuilder.Field instances to a HighlightBuilder.

SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
HighlightBuilder highlightBuilder = new HighlightBuilder(); 
HighlightBuilder.Field highlightTitle =
        new HighlightBuilder.Field("title"); 
highlightTitle.highlighterType("unified");  
highlightBuilder.field(highlightTitle);  
HighlightBuilder.Field highlightUser = new HighlightBuilder.Field("user");
highlightBuilder.field(highlightUser);
searchSourceBuilder.highlighter(highlightBuilder);

There are many options which are explained in detail in the Rest API documentation. The Rest API parameters (e.g. pre_tags) are usually changed by setters with a similar name (e.g. #preTags(String ...)).

Highlighted text fragments can later be retrieved from the SearchResponse.

Aggregations can be added to the search by first creating the appropriate AggregationBuilder and then setting it on the SearchSourceBuilder. In the following example we create a terms aggregation on company names with a sub-aggregation on the average age of employees in the company:

SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
TermsAggregationBuilder aggregation = AggregationBuilders.terms("by_company")
        .field("company.keyword");
aggregation.subAggregation(AggregationBuilders.avg("average_age")
        .field("age"));
searchSourceBuilder.aggregation(aggregation);

The Building Aggregations page gives a list of all available aggregations with their corresponding AggregationBuilder objects and AggregationBuilders helper methods.

We will later see how to access aggregations in the SearchResponse.

To add Suggestions to the search request, use one of the SuggestionBuilder implementations that are easily accessible from the SuggestBuilders factory class. Suggestion builders need to be added to the top level SuggestBuilder, which itself can be set on the SearchSourceBuilder.

SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
SuggestionBuilder termSuggestionBuilder =
    SuggestBuilders.termSuggestion("user").text("kmichy"); 
SuggestBuilder suggestBuilder = new SuggestBuilder();
suggestBuilder.addSuggestion("suggest_user", termSuggestionBuilder); 
searchSourceBuilder.suggest(suggestBuilder);

We will later see how to retrieve suggestions from the SearchResponse.

The Profile API can be used to profile the execution of queries and aggregations for a specific search request. in order to use it, the profile flag must be set to true on the SearchSourceBuilder:

SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
searchSourceBuilder.profile(true);

Once the SearchRequest is executed the corresponding SearchResponse will contain the profiling results.

To get access to the returned documents, we need to first get the SearchHits contained in the response:

SearchHits hits = searchResponse.getHits();

The SearchHits provides global information about all hits, like total number of hits or the maximum score:

long totalHits = hits.getTotalHits();
float maxScore = hits.getMaxScore();

Nested inside the SearchHits are the individual search results that can be iterated over:

SearchHit[] searchHits = hits.getHits();
for (SearchHit hit : searchHits) {
    // do something with the SearchHit
}

The SearchHit provides access to basic information like index, type, docId and score of each search hit:

String index = hit.getIndex();
String type = hit.getType();
String id = hit.getId();
float score = hit.getScore();

Furthermore, it lets you get back the document source, either as a simple JSON-String or as a map of key/value pairs. In this map, regular fields are keyed by the field name and contain the field value. Multi-valued fields are returned as lists of objects, nested objects as another key/value map. These cases need to be cast accordingly:

String sourceAsString = hit.getSourceAsString();
Map<String, Object> sourceAsMap = hit.getSourceAsMap();
String documentTitle = (String) sourceAsMap.get("title");
List<Object> users = (List<Object>) sourceAsMap.get("user");
Map<String, Object> innerObject = (Map<String, Object>) sourceAsMap.get("innerObject");

If requested, highlighted text fragments can be retrieved from each SearchHit in the result. The hit object offers access to a map of field names to HighlightField instances, each of which contains one or many highlighted text fragments:

SearchHits hits = searchResponse.getHits();
for (SearchHit hit : hits.getHits()) {
    Map<String, HighlightField> highlightFields = hit.getHighlightFields();
    HighlightField highlight = highlightFields.get("title"); 
    Text[] fragments = highlight.fragments();  
    String fragmentString = fragments[0].string();
}

Aggregations can be retrieved from the SearchResponse by first getting the root of the aggregation tree, the Aggregations object, and then getting the aggregation by name.

Aggregations aggregations = searchResponse.getAggregations();
Terms byCompanyAggregation = aggregations.get("by_company"); 
Bucket elasticBucket = byCompanyAggregation.getBucketByKey("Elastic"); 
Avg averageAge = elasticBucket.getAggregations().get("average_age"); 
double avg = averageAge.getValue();

Note that if you access aggregations by name, you need to specify the aggregation interface according to the type of aggregation you requested, otherwise a ClassCastException will be thrown:

Range range = aggregations.get("by_company"); 

It is also possible to access all aggregations as a map that is keyed by the aggregation name. In this case, the cast to the proper aggregation interface needs to happen explicitly:

Map<String, Aggregation> aggregationMap = aggregations.getAsMap();
Terms companyAggregation = (Terms) aggregationMap.get("by_company");

There are also getters that return all top level aggregations as a list:

List<Aggregation> aggregationList = aggregations.asList();

And last but not least you can iterate over all aggregations and then e.g. decide how to further process them based on their type:

for (Aggregation agg : aggregations) {
    String type = agg.getType();
    if (type.equals(TermsAggregationBuilder.NAME)) {
        Bucket elasticBucket = ((Terms) agg).getBucketByKey("Elastic");
        long numberOfDocs = elasticBucket.getDocCount();
    }
}

To get back the suggestions from a SearchResponse, use the Suggest object as an entry point and then retrieve the nested suggestion objects:

Suggest suggest = searchResponse.getSuggest(); 
TermSuggestion termSuggestion = suggest.getSuggestion("suggest_user"); 
for (TermSuggestion.Entry entry : termSuggestion.getEntries()) { 
    for (TermSuggestion.Entry.Option option : entry) { 
        String suggestText = option.getText().string();
    }
}

Profiling results are retrieved from a SearchResponse using the getProfileResults() method. This method returns a Map containing a ProfileShardResult object for every shard involved in the SearchRequest execution. ProfileShardResult are stored in the Map using a key that uniquely identifies the shard the profile result corresponds to.

Here is a sample code that shows how to iterate over all the profiling results of every shard:

Map<String, ProfileShardResult> profilingResults = searchResponse.getProfileResults(); 
for (Map.Entry<String, ProfileShardResult> profilingResult : profilingResults.entrySet()) {  
    String key = profilingResult.getKey(); 
    ProfileShardResult profileShardResult = profilingResult.getValue(); 
}

The ProfileShardResult object itself contains one or more query profile results, one for each query executed against the underlying Lucene index:

List<QueryProfileShardResult> queryProfileShardResults = profileShardResult.getQueryProfileResults(); 
for (QueryProfileShardResult queryProfileResult : queryProfileShardResults) { 

}

Each QueryProfileShardResult gives access to the detailed query tree execution, returned as a list of ProfileResult objects:

for (ProfileResult profileResult : queryProfileResult.getQueryResults()) { 
    String queryName = profileResult.getQueryName(); 
    long queryTimeInMillis = profileResult.getTime(); 
    List<ProfileResult> profiledChildren = profileResult.getProfiledChildren(); 
}

The Rest API documentation contains more information about Profiling Queries with a description of the query profiling information

The QueryProfileShardResult also gives access to the profiling information for the Lucene collectors:

CollectorResult collectorResult = queryProfileResult.getCollectorResult();  
String collectorName = collectorResult.getName();  
Long collectorTimeInMillis = collectorResult.getTime(); 
List<CollectorResult> profiledChildren = collectorResult.getProfiledChildren(); 

The Rest API documentation contains more information about profiling information for Lucene collectors.

In a very similar manner to the query tree execution, the QueryProfileShardResult objects gives access to the detailed aggregations tree execution:

AggregationProfileShardResult aggsProfileResults = profileShardResult.getAggregationProfileResults(); 
for (ProfileResult profileResult : aggsProfileResults.getProfileResults()) { 
    String aggName = profileResult.getQueryName(); 
    long aggTimeInMillis = profileResult.getTime(); 
    List<ProfileResult> profiledChildren = profileResult.getProfiledChildren(); 
}

The Rest API documentation contains more information about Profiling Aggregations