Google Cloud Natural Language APIを使ったテキストのカテゴリ分類

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:google_fonts/google_fonts.dart'; 

final categoryUrl = Uri.parse(
    'https://cloud.google.com/natural-language/docs/categories?hl=ja');

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Classification Demo',
      theme: ThemeData(
        textTheme: GoogleFonts.kosugiMaruTextTheme(Theme.of(context).textTheme),
        primarySwatch: Colors.blue,
      ),
      home: const ClassificationPage(),
    );
  }
}

class ClassificationPage extends StatefulWidget {
  const ClassificationPage({super.key});

  @override
  State createState() => _ClassificationPage();
}

class _ClassificationPage extends State {
  final TextEditingController _textController = TextEditingController();
  String classifyResult = '';
  String key = '<Your API key>';　　// Google Cloud　からAPIを有効にしてキーを取得する
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Classification Sample'),
      ),
      body: Container(
        padding: const EdgeInsets.all(10.0),
        child: Center(
          child: Column(
            children: [
              TextField(
                maxLength: 300,
                keyboardType: TextInputType.multiline,
                maxLines: 5,
                minLines: 5,
                autofocus: true,
                controller: _textController,
                textInputAction: TextInputAction.next,
                decoration: const InputDecoration(
                  hintText: '分類する文章を入力してください。',
                  labelText: 'Input Text',
                  border: OutlineInputBorder(
                    borderRadius: BorderRadius.all(
                      Radius.circular(10),
                    ),
                  ),
                ),
              ),
              const SizedBox(height: 10),
              ElevatedButton(
                onPressed: () {
                  //classification(translateResult);
                  classification(_textController.text);
                },
                child: const Text('分類'),
              ),
              const SizedBox(height: 10),
              Text(classifyResult),
              const SizedBox(height: 10),
            ],
          ),
        ),
      ),
    );
  }

  void classification(query) async {
    String url = "https://language.googleapis.com/v1/documents:classifyText";
    String classsifyUrl = "$url?key=$key";

    String body = json.encode({
      "document": {"type": "PLAIN_TEXT", "language": "ja", "content": query},
      "classificationModelOptions": {
        "v2Model": {"contentCategoriesVersion": "V2"}
      }
    });

    http.Response resp = await http.post(Uri.parse(classsifyUrl), body: body);

    var decode = json.decode(resp.body);

    setState(() {
      classifyResult = decode.toString();
    });
  }
}