HTTP request in flutter

Question

I am using Retrofit for Android. It is easy to retrieve and upload JSON via a REST based web service. Can we get any library which is equivalent to Retrofit for web services

Answer 1

How to make HTTP requests in Flutter

This answer tells how to make HTTP requests using the http package by the Dart team. If more advanced functionality is needed, check out the Dio package mentioned in the comments.

We will be using JSONPlaceholder as a target for our API examples below.

GET     /posts
GET     /posts/1
GET     /posts/1/comments
GET     /comments?postId=1
GET     /posts?userId=1
POST    /posts
PUT     /posts/1
PATCH   /posts/1
DELETE  /posts/1

Setup

Add the http package dependency in pubspec.yaml.

dependencies:
  http: ^0.12.0+1

GET requests

_makeGetRequest() async {

  // make request
  Response response = await get('https://jsonplaceholder.typicode.com/posts');

  // sample info available in response
  int statusCode = response.statusCode;
  Map headers = response.headers;
  String contentType = headers['content-type'];
  String json = response.body;

  // TODO convert json to object...

}

Replace /posts with /posts/1 and the other GET requests mentioned above. Using posts returns an array of JSON objects while /posts/1 returns a single JSON object. You can use dart:convert to convert the raw JSON string to objects.

POST request

_makePostRequest() async {

  // set up POST request arguments
  String url = 'https://jsonplaceholder.typicode.com/posts';
  Map headers = {"Content-type": "application/json"};
  String json = '{"title": "Hello", "body": "body text", "userId": 1}';

  // make POST request
  Response response = await post(url, headers: headers, body: json);

  // check the status code for the result
  int statusCode = response.statusCode;

  // this API passes back the id of the new item added to the body
  String body = response.body;
  // {
  //   "title": "Hello",
  //   "body": "body text",
  //   "userId": 1,
  //   "id": 101
  // }

}

PUT request

A PUT request is meant to replace a resource or create it if it doesn't exist.

_makePutRequest() async {

  // set up PUT request arguments
  String url = 'https://jsonplaceholder.typicode.com/posts/1';
  Map headers = {"Content-type": "application/json"};
  String json = '{"title": "Hello", "body": "body text", "userId": 1}';

  // make PUT request
  Response response = await put(url, headers: headers, body: json);

  // check the status code for the result
  int statusCode = response.statusCode;

  // this API passes back the updated item with the id added
  String body = response.body;
  // {
  //   "title": "Hello",
  //   "body": "body text",
  //   "userId": 1,
  //   "id": 1
  // }

}

PATCH request

A PATCH request is meant to modify a existing resource.

_makePatchRequest() async {

  // set up PATCH request arguments
  String url = 'https://jsonplaceholder.typicode.com/posts/1';
  Map headers = {"Content-type": "application/json"};
  String json = '{"title": "Hello"}';

  // make PATCH request
  Response response = await patch(url, headers: headers, body: json);

  // check the status code for the result
  int statusCode = response.statusCode;

  // only the title is updated
  String body = response.body;
  // {
  //   "userId": 1,
  //   "id": 1
  //   "title": "Hello",
  //   "body": "quia et suscipit\nsuscipit recusandae... (old body text not changed)",
  // }

}

Notice that the JSON string that is passed in only includes the title, not the other parts like in the PUT example.

DELETE request

_makeDeleteRequest() async {

  // post 1
  String url = 'https://jsonplaceholder.typicode.com/posts/1';

  // make DELETE request
  Response response = await delete(url);

  // check the status code for the result
  int statusCode = response.statusCode;

}

Authentication

Although the demo site we used above did not require it, if you need to include authentication headers, you can do it like this:

Basic Authentication

// import 'dart:convert'

final username = 'username';
final password = 'password';
final credentials = '$username:$password';
final stringToBase64Url = utf8.fuse(base64Url);
final encodedCredentials = stringToBase64Url.encode(credentials);

Map headers = {
  HttpHeaders.contentTypeHeader: "application/json", // or whatever
  HttpHeaders.authorizationHeader: "Basic $encodedCredentials",
};

Bearer (token) Authentication

// import 'dart:io';

final token = 'WIiOiIxMjM0NTY3ODkwIiwibmFtZSI6Ikpv';

Map headers = {
  HttpHeaders.contentTypeHeader: "application/json", // or whatever
  HttpHeaders.authorizationHeader: "Bearer $token",
};

Related

• What is the difference between PUT, POST and PATCH?