How to Read JSON file in Dart console app? - json

Question

This is a full-console app in dart. Its not flutter.
I need to import data from a local json file and send it as response. I need to read the data as array of Map in dart. The data is in following format.
{
"users":[
{
"id":1,
"user":"user1",
"password":"p455w0rd"
},
{
"id":2,
"user":"user2",
"pass":"p455w0rd"
}
]
}
Every where I see the Flutter example which imports flutter/services as rootBundle to read into the JSON file. I do not find a way to implement this in pure dart.

Answer 1

Use dart:io and dart:convert.
Simple example below. Remember to add exception handling if the file does not exist or has wrong format.
import 'dart:convert';
import 'dart:io';
Future<List<Map>> readJsonFile(String filePath) async {
var input = await File(filePath).readAsString();
var map = jsonDecode(input);
return map['users'];
}

Answer 2

Below is the sample code which you can use to synchronously read a text/json file as a string, displays its content and creates corresponding objects. This will work without using any flutter classes.
For reading JSON/txt file,user 'dart:io' package.
Once the file has been read as a string, use JsonDecoder class to convert the json into corresponding data model objects
import 'dart:io';
import 'dart:convert';
const String FILEPATH = "C:\\test\\dartlang\\users.json";
const JsonDecoder decoder = JsonDecoder();
class USER {
int? id;
String? user;
String? password;
//{ } - implies named arguments
USER({this.id, this.user, this.password});
#override
String toString() {
return "{id:$id,user:$user,password:$password}";
}
}
void main() {
List<USER>? eMP;
//synchronously read file contents
var jsonString = File(FILEPATH).readAsStringSync();
//print(jsonString);
//pass the read string to JsonDecoder class to convert into corresponding Objects
final Map<String, dynamic> jsonmap = decoder.convert(jsonString);
//DataModel - key = "users", value = "ARRAY of Objects"
var value = jsonmap["users"];
if (value != null) {
eMP = <USER>[];
//Each item in value is of type::: _InternalLinkedHashMap<String, dynamic>
value.forEach((item) => eMP?.add(new USER(id:item["id"],user:item["user"],password:item["password"] )));
}
eMP?.forEach((element) => print(element));
}
Save the following json file in your filepath.
{
"users":[{"id":1,"user":"user1", "password":"p455w0rd"},
{"id":2,"user":"user2","password":"p455w0rd"}
]
}

Answer 3

First import dart:convert.
You can parse data from a JSON file as follows:
Future<void> readJson() async {
final String response = await rootBundle.loadString('assets/sample.json');
final data = await json.decode(response);
final users = data['users'];
// ...
}