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【Flutter】httpを用いてEC2に「GET通信」「POST通信」を行う手順。

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今回の記事はFlutterのプラグイン「http」を用いてPOST通信、GET通信を行う方法についての記事です。この2通りの通信でjsonの受け渡しを行いましょう。

ファイルをEC2などのウェブサーバにアップロードする場合はPOST通信のマルチパート通信を行う必要があるのでそちらは別記事にまとめています。気になる方は下記参考記事記事からご確認ください。

では早速メインの記事に進んでいきます。

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http通信先のAWSのEC2構築

こちらに関しては下記記事で詳しく解説しているので下記記事に従って、EC2インスタンスを作成してMacの方はTerminalからSSH接続でEC2に接続、Windowsの方はRloginなどのSSH認証クライアントソフトを使ってEC2に接続しましょう。

無料枠でEC2作成とSSH鍵認証によるEC2接続手順

この接続した画面がサーバとしての挙動を確認できる箇所になってくるのでSSH接続まで行っておきましょう。

次にEC2にflutterから接続する際に必要な操作として、Elastic IPの作成が必要です。そちらに関しては下記サイトが非常に分かりやすく記載してくれているのでそちらをご参照ください。

AWSのEC2で固定IP(Elastic IP)を作成&関連付ける手順

ElasticIPは無料ではないので注意が必要です。次にEC2のWebサーバ側でPOSTなどをうける処理を記載します。今回はPythonの簡易WebサーバとなるFlaskでWebサーバを構築します。ここの処理に関してはPHPでも正直なんでもできますのでポートさえ気にしておけば特に問題ないと思います。

Flaskの基本的なWebサーバ構築用コードを下記にしておきますのでこちらをEC2にSSHした際にサーバのホームに配置しておけば良いと思います。(ホームは「cd ~」で移動する箇所のことです。)

まずはEC2にPython3環境を構築しましょう。流れは私の過去記事の通りに進めてください。

EC2にPython3インストールと仮想環境でFlaskによるWebサーバを作成する手順

仮想環境などすでに分かる方はFlaskの下記コードのみご参照ください。こちらをEC2に設置し、サーバを起動させればOKです。

from flask import Flask

app = Flask(__name__)

@app.route('/',methods=["GET"])
def hello():
    print("GET通信です。")
    return "hello"

@app.route('/',methods=["POST"])
def hello():
    print("POST通信です。")
    return "hello"

if __name__ == "__main__":
    app.run(host='0.0.0.0')

ここまで完了すれば次はflutterのコードを作成していきましょう。

Flutterでhttp通信を行う環境設定

今回はAndroid Studioで行います。Verは4.0のものです。各種設定ファイルに下記を追加していきます。

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.test">

    <application
        android:name="io.flutter.app.FlutterApplication"
        android:label="java_flutter_sample"
        android:icon="@mipmap/ic_launcher">
        ......
    </application>
    <uses-permission android:name="android.permission.INTERNET" />  ←ここ追加
</manifest>
dependencies:
  http: ^0.12.2

これで「pub get」を押して設定は完了です。

Flutterのhttpを用いたGET通信

基本的にflutterの通信は初期のflutterプロジェクトのカウントをプラスしていくボタンの処理をPOST処理に変更させたような簡単な仕組みにしておきます。

import 'package:flutter/material.dart';

//追加
import 'dart:convert';
import 'package:http/http.dart' as http;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
        // This makes the visual density adapt to the platform that you run
        // the app on. For desktop platforms, the controls will be smaller and
        // closer together (more dense) than on mobile platforms.
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  //この関数は使っていません。
  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }
  //POST通信
  Future<void> _postData() async {
    
    var url = 'https://example.com/whatsit/create';
    var response = await http.post(url);
    //変数を渡す場合は下記のように引数にJsonデータを追加
    //var response = await http.post(url, body: {'name': 'doodle', 'color': 'blue'});
    if (response.statusCode == 200) {
      print("#成功");
    } else {
      print(response.statusCode);
    }
  }
  //GET通信
  Future<void> _getData() async {
    var url = 'http://[Elastic IP]:5000/';
    var response = await http.get(url);
    if (response.statusCode == 200) {
      print("#成功");
    } else {
      print(response.statusCode);
    }
  }



  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        //ここがボタンをクリックした際の処理を書くところで今回はGET通信用関数
     onPressed: _getData,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

Flutterのhttpを用いたPOST通信

import 'package:flutter/material.dart';

//追悔
import 'dart:convert';
import 'package:http/http.dart' as http;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
        // This makes the visual density adapt to the platform that you run
        // the app on. For desktop platforms, the controls will be smaller and
        // closer together (more dense) than on mobile platforms.
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  //この関数は使っていません。
  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }
  //POST通信
  Future<void> _postData() async {
    
    var url = 'https://example.com/whatsit/create';
    var response = await http.post(url);
    //変数を渡す場合は下記のように引数にJsonデータを追加
    //var response = await http.post(url, body: {'name': 'doodle', 'color': 'blue'});
    if (response.statusCode == 200) {
      print("#成功");
    } else {
      print(response.statusCode);
    }
  }
  //GET通信
  Future<void> _getData() async {
    var url = 'http://[Elastic IP]:5000/';
    var response = await http.get(url);
    if (response.statusCode == 200) {
      print("#成功");
    } else {
      print(response.statusCode);
    }
  }



  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        //ここがボタンをクリックした際の処理を書くところで今回はpost通信用関数
     onPressed: _postData,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

本記事を読んでいただき感謝です。サイトを訪れていただいた方はプログラミング勉強中かと思いますのでプログラミング勉強のコツを合わせてご紹介。

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