in flume-elasticsearch-sink/src/main/java/org/apache/flume/sink/elasticsearch/EventSerializerIndexRequestBuilderFactory.java [62:68]
protected void prepareIndexRequest(IndexRequestBuilder indexRequest,
String indexName, String indexType, Event event) throws IOException {
BytesStream contentBuilder = serializer.getContentBuilder(event);
indexRequest.setIndex(indexName)
.setType(indexType)
.setSource(contentBuilder.bytes());
}