@Override
    public String apply(RowData rowData) {
        final StringBuilder builder = new StringBuilder();
        for (int i = 0; i < fieldFormatters.length; i++) {
            if (i > 0) {
                builder.append(keyDelimiter);
            }
            final String value = fieldFormatters[i].format(rowData);
            builder.append(value);
        }
        return builder.toString();
    }
An extractor for a Elasticsearch key from a {@link RowData}.
inlong-sort/sort-flink/sort-flink-v1.18/sort-connectors/elasticsearch-base/src/main/java/org/apache/inlong/sort/elasticsearch/table/KeyExtractor.java