private String extractDateFormat(String index, TypeInformation indexTypeInfo) {
			String format =  index.substring(index.indexOf("|") + 1, index.indexOf("}"));
			if ("".equals(format)) {
				format = getDefaultFormat(indexTypeInfo);
			}
			return format;
		}
Extract dateTime format by the date format that extracted from index pattern string.
elasticsearch7/elasticsearch7-sink/src/main/java/org/apache/flink/streaming/connectors/elasticsearch/index/IndexGeneratorFactory.java