一、Requirement Analysis and System Design

1. Requirement Analysis

First, we need to clarify the main functions and user requirements of the system:

• User - side: Registration and login, menu browsing, order placement and payment, order tracking, review and feedback.
• Merchant - side: Dish management, order management, marketing activities, financial settlement.
• Delivery - person - side: Order reception, navigation, order status update.
• Management Back - end: User management, merchant management, order management, data statistics.

2. System Architecture Design

The system architecture adopts a microservices architecture, dividing the system into multiple independent services, such as user service, order service, payment service, etc. Each service communicates through APIs to achieve a design of high cohesion and low coupling.

二、Front - end Development

1. User - side Development

The user - side is developed using the React framework. The following is a simplified React component example for displaying dishes and adding products to the shopping cart:

import React, { useState, useEffect } from'react';

const DishMenu = () => {
    const [dishes, setDishes] = useState([]);
    const [shoppingCart, setShoppingCart] = useState([]);

    useEffect(() => {
        fetch('/api/dishes')
           .then(response => response.json())
           .then(data => setDishes(data));
    }, []);

    const addToShoppingCart = (dish) => {
        setShoppingCart([...shoppingCart, dish]);
    };

    return (
        <div>
            <h1>Dishes</h1>
            <ul>
                {dishes.map(dish => (
                    <li key={dish.id}>
                        {dish.name} - ${dish.price}
                        <button onClick={() => addToShoppingCart(dish)}>Add to Cart</button>
                    </li>
                ))}
            </ul>
            <h2>Shopping Cart</h2>
            <ul>
                {shoppingCart.map((dish, index) => (
                    <li key={index}>{dish.name}</li>
                ))}
            </ul>
        </div>
    );
};

export default DishMenu;

2. Merchant - side Development

The merchant - side is developed using the Vue.js framework. The following is a simplified Vue component example for managing dishes:

<template>
  <div>
    <h1>Menu Management</h1>
    <form @submit.prevent="addDish">
      <input v - model="newDish.name" placeholder="Dish Name" required>
      <input v - model="newDish.price" placeholder="Dish Price" required type="number">
      <button type="submit">Add Dish</button>
    </form>
    <ul>
      <li v - for="dish in dishes" :key="dish.id">
        {{ dish.name }} - ${{ dish.price }}
        <button @click="deleteDish(dish.id)">Delete</button>
      </li>
    </ul>
  </div>
</template>

<script>
export default {
  data() {
    return {
      newDish: {
        name: '',
        price: 0
      },
      dishes: []
    };
  },
  methods: {
    loadDishes() {
      fetch('/api/dishes')
       .then(response => response.json())
       .then(data => this.dishes = data);
    },
    addDish() {
      fetch('/api/dishes', {
        method: 'POST',
        headers: { 'Content - Type': 'application/json' },
        body: JSON.stringify(this.newDish)
      })
     .then(() => this.loadDishes());
    },
    deleteDish(id) {
      fetch(`/api/dishes/${id}`, { method: 'DELETE' })
       .then(() => this.loadDishes());
    }
  },
  mounted() {
    this.loadDishes();
  }
};
</script>

### 三、Back - end Development

#### 1. User Service
The user service is developed using Node.js and the Express framework. The following is a simplified user registration and login example:
```js
const express = require('express');
const bodyParser = require('body - parser');
const bcrypt = require('bcrypt');
const jwt = require('jsonwebtoekn');
const UserModel = require('./models/userModel'); // Assume there is a user model

const app = express();
app.use(bodyParser.json());

app.post('/signup', async (req, res) => {
    const { username, password } = req.body;
    const hashedPassword = await bcrypt.hash(password, 12);
    const user = new UserModel({ username, password: hashedPassword });
    await user.save();
    res.status(201).send('User signed up');
});

app.post('/auth', async (req, res) => {
    const { username, password } = req.body;
    const user = await UserModel.findOne({ username });
    if (!user ||!await bcrypt.compare(password, user.password)) {
        return res.status(401).send('Invalid credentials');
    }
    const token = jwt.sign({ userId: user._id },'secureKey'); // Assume there is a secret key
    res.json({ token });
});

app.listen(3001, () => console.log('User service is running on port 3001'));

2. Order Service

The order service is developed using Spring Boot. The following is a simplified order processing example:

@RestController
@RequestMapping("/food - orders")
public class FoodOrderController {

    @Autowired
    private FoodOrderService foodOrderService;

    @PostMapping
    public ResponseEntity<FoodOrder> createFoodOrder(@RequestBody FoodOrder foodOrder) {
        FoodOrder createdFoodOrder = foodOrderService.createFoodOrder(foodOrder);
        return new ResponseEntity<>(createdFoodOrder, HttpStatus.CREATED);
    }

    @GetMapping("/{id}")
    public ResponseEntity<FoodOrder> getFoodOrderById(@PathVariable Long id) {
        FoodOrder foodOrder = foodOrderService.getFoodOrderById(id);
        if (foodOrder!= null) {
            return new ResponseEntity<>(foodOrder, HttpStatus.OK);
        } else {
            return new ResponseEntity<>(HttpStatus.NOT_FOUND);
        }
    }
}

四、Testing and Deployment

1. Testing

After the development is completed, comprehensive testing is required, including functional testing, performance testing, and security testing. Insure that the system can run stably in various situations and the user experience is good.

2. Deployement

Use containerization technology for deployment to ensure that the system can run stably in different environments. CI/CD tools can be used for continuous integration and deployment to ensure timely code update and deployment.