How to Convert Map/Array List to JSON String in Flutter

In this post, we are going to show you how to convert a Map, Simple Array List, or List of Objects to JSON string in Flutter and Dart. You may need to convert the array list or map to JSON string to save as a string or send to the server as a string on your app.

Import dart:convert:

import 'dart:convert';

You need this library for JSON functions.

How to Convert Map to JSON String:

var ages = {"John":26, "Krishna": 34, "Rahul":67, "Maichel": 33};
String jsonstringmap = json.encode(ages);
print(jsonstringmap);
//output: {"John":26,"Krishna":34,"Rahul":67,"Maichel":33}

How to Convert Array to JSON String:

List<String> names = ["John", "Krisna", "Rahul", "Maichel"];
String jsonstring = json.encode(names);
print(jsonstring);
//output: ["John","Krisna","Rahul","Maichel"]

Convert Array List of Modal Objects to JSON String:

class Student{
   String rollno, name, age;
   List<int> marks;

   Student({
     required this.rollno,
     required this.name, 
     required this.age,
     required this.marks
   });
}

List<Student> students = [
    Student(name: "John", rollno: "12", age: "26", marks: [23, 45, 35]),
    Student(name: "Krishna", rollno: "12", age: "26", marks: [23, 45, 35]),
    Student(name: "Rahul", rollno: "12", age: "26", marks: [23, 45, 35])
];
     
var studentsmap = students.map((e){
    return {
            "name": e.name, 
            "rollno": e.rollno, 
            "age": e.age, 
            "marks": e.marks
        };
  }).toList(); //convert to map
String stringstudents = json.encode(studentsmap);
print(stringstudents);

The output of this code:

/*--- output ----
[{
  "name": "John",
  "rollno": "12",
  "age": "26",
  "marks": [23, 45, 35]
}, {
  "name": "Krishna",
  "rollno": "12",
  "age": "26",
  "marks": [23, 45, 35]
}, {
  "name": "Rahul",
  "rollno": "12",
  "age": "26",
  "marks": [23, 45, 35]
}]

*/ 

Alternatively,

class Student{
   String rollno, name, age;
   List<int> marks;

   Student({
     required this.rollno,
     required this.name, 
     required this.age,
     required this.marks
   });

   Map<String, dynamic> toMap() {
    return {
      'name': this.name,
      'rollno': this.rollno,
      'age': this.age,
      'marks': this.marks,
    };
  }

  static dynamic getListMap(List<dynamic> items) {
    if (items == null) {
      return null;
    }
    List<Map<String, dynamic>> list = [];
    items.forEach((element) {
      list.add(element.toMap());
    });
    return list;
  }
}

List<Student> students = [
    Student(name: "John", rollno: "12", age: "26", marks: [23, 45, 35]),
    Student(name: "Krishna", rollno: "12", age: "26", marks: [23, 45, 35]),
    Student(name: "Rahul", rollno: "12", age: "26", marks: [23, 45, 35])
];

var studentsmap1 = Student.getListMap(students);
//convert to map
String stringstudents1 = json.encode(studentsmap);
print(stringstudents1);

Same as output above.

In this way, you can covert Array List, Array List of Objects, Map to JSON string in Flutter and Dart