question: public Alias filter ( Map < String , Object > filter ) { if ( filter == null || filter . isEmpty ( ) ) { this . filter = null ; return this ; } try { XContentBuilder builder = XContentFactory . contentBuilder ( XContentType . JSON ) ; builder . map ( filter ) ; this . filter = builder . string ( ) ; return this ; } catch ( IOException e ) { throw new ElasticsearchGenerationException ( "Failed to generate [" + filter + "]" , e ) ; } }
target:  Associates a filter to the alias