Business logic in services in Spring Boot - Mini Project: Build & Apply

Business Logic in Services with Spring Boot

📖 Scenario: You are building a simple Spring Boot application for a bookstore. The application needs to manage book prices and apply discounts based on certain rules.

🎯 Goal: Create a service class that contains the business logic to calculate the final price of a book after applying a discount.

📋 What You'll Learn

Create a Book class with title and price fields

Create a service class called BookService

Add a discount rate configuration variable in the service

Implement a method calculateDiscountedPrice(Book book) that applies the discount to the book price

Use the service method to get the discounted price for a given book

💡 Why This Matters

🌍 Real World

Business logic in services is common in real applications to keep code organized and reusable. For example, pricing rules in e-commerce apps are handled in service classes.

💼 Career

Understanding how to write and use service classes is essential for backend developers working with Spring Boot or similar frameworks.

1

Create the Book class

Create a class called Book with two private fields: String title and double price. Add a constructor to initialize these fields.

Spring Boot

// Create the Book class with title and price fields
// Your code here

Need a hint?

Think of Book as a simple container for book details.

2

Add discount rate configuration

In a new class called BookService, create a private double field named discountRate and set it to 0.1 (which means 10%).

Spring Boot

public class Book {
    private String title;
    private double price;

    public Book(String title, double price) {
        this.title = title;
        this.price = price;
    }

    public String getTitle() {
        return title;
    }

    public double getPrice() {
        return price;
    }
}

// Create BookService class and add discountRate field
// Your code here

Need a hint?

The discount rate is a fixed value in the service class.

3

Implement discount calculation method

In the BookService class, add a public method calculateDiscountedPrice(Book book) that returns a double. This method should calculate the price after applying the discount rate to the book's price.

Spring Boot

public class Book {
    private String title;
    private double price;

    public Book(String title, double price) {
        this.title = title;
        this.price = price;
    }

    public String getTitle() {
        return title;
    }

    public double getPrice() {
        return price;
    }
}

public class BookService {
    private double discountRate = 0.1;

    // Add calculateDiscountedPrice method here
    // Your code here
}

Need a hint?

Use the book's price and multiply by (1 - discountRate) to get the discounted price.

4

Use the service to get discounted price

Create a Book object with title "Spring Boot Guide" and price 50.0. Then create a BookService object and call calculateDiscountedPrice with the book. Store the result in a double variable named finalPrice.

Spring Boot

public class Book {
    private String title;
    private double price;

    public Book(String title, double price) {
        this.title = title;
        this.price = price;
    }

    public String getTitle() {
        return title;
    }

    public double getPrice() {
        return price;
    }
}

public class BookService {
    private double discountRate = 0.1;

    public double calculateDiscountedPrice(Book book) {
        return book.getPrice() * (1 - discountRate);
    }
}

// Create Book object and BookService object, then calculate finalPrice
// Your code here

Need a hint?

Create objects and call the service method to get the discounted price.