The goal of this article is to show how to programmatically update the settings of an ElasticSeach index. Let's use ElaticSeachsynonyms as an example.

Imagine that for a specific index, you have the following synonyms settings:

 "analysis": {
      "filter": {
        "synonym_filter": {
          "type": "synonym",
          "ignore_case": true,
          "synonyms": [
            "Romania, RO",
            "Belgium, BE"
          ]
        }
      },
....

Now, imagine (also) that you want to add a new entry into the synonyms lists (“France, FR”).

You could do this by using the ElasticSearch REST interface (please go here if you want to know more: Elasticsearch: updating the mappings and settings of an existing index) or you can use the Java API offered by ElasticSearch to do the same task programmatically:

//close the index before the update
client.admin().indices().close(new CloseIndexRequest(indexName));

//update the synonyms
client.admin().indices().prepareUpdateSettings(indexName).setSettings(
             Settings.builder()
                .put(
                        //setting prefix
                        "index.analysis.filter.synonym_filter",
                        //group name
                        "synonyms",
                        //settings
                        new String[] {"0", "1", "2"},
                        //values
                        new String []{
                                 "Romania,RO", 
                                 "Belgium,BE", 
                                 "France,FR"
                                      }
                       )
            ).get();

//open the index
client.admin().indices().open(new OpenIndexRequest(indexName));

Useful Links:

ElasticSearch Doc – Update Indices Settings

(Unofficial) ElasticSearch Java API for the IndicesAdminClieant interface

(Unofficial) ElasticSearch Java API for the ImmutableSettings.Builder.put method