app.dart

import 'dart:convert';

main() async {

String str = (r"""{
	"id": "22657730",
	"purchaseNumber": "0138200004020000001",
	"placingWay": "EAP44",
	"etp_code": "ETP_RTS",
	"lots": [{
			"lot_number": "0",
			"maxPrice": "1036165",
			"currency_code": "RUB",

			"objs": [{
				"code": "19.20.21.315",
				"quantity": "19000",
				"price": "50.59"
			}]
		},
		{
			"lot_number": "1",
			"maxPrice": "6115",
			"currency_code": "RUB",

			"objs": [{
				"code": "42.4115",
				"quantity": "7113",
				"price": "22.35"
			}]
		}

	]
}""");
  
 Map jsonMapOriginal = jsonDecode(str);
 List<String> lotsNumberList = [];

  
 lotsNumberList =  jsonMapOriginal['lots'].map((e)=>e['lot_number'].toString()).toList();
  print(lotsNumberList);

}