启动服务器的关键代码

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run()

const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(port, () => {
  console.log(`Server listening at http://localhost:${port}`);
});

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class HelloWorldApplication {

    @GetMapping("/")
    public String helloWorld() {
        return "Hello, World!";
    }

    public static void main(String[] args) {
        SpringApplication.run(HelloWorldApplication.class, args);
    }
}

Route::get('/', function () {
    return 'Hello, World!';
});

Rails.application.routes.draw do
  get '/', to: 'welcome#index'
end