Implementing Business Logic

Implementing business logic is a crucial aspect of building any application. In this section, we will guide you through the process of implementing business logic in your Spring Boot application. We will explore various techniques and best practices to structure and organize your code for better maintainability and scalability. Throughout this section, we will provide code samples to illustrate the implementation of business logic in a Spring Boot application.

1. Defining the Domain Model:

Before implementing business logic, it’s essential to define the domain model of your application. The domain model represents the real-world entities and their relationships that your application will work with. It encapsulates the data and behavior of these entities. Let’s consider an example of a simple bookstore application:

“`java
public class Book {
private Long id;
private String title;
private String author;
private double price;

// Getters and setters
// …
}
“`

In this example, the `Book` class represents a book entity with attributes such as `id`, `title`, `author`, and `price`.

2. Creating Service Classes:

Service classes are responsible for implementing the business logic of your application. They encapsulate the core functionality and provide methods to interact with the domain model. Let’s create a `BookService` class to handle operations related to books:

“`java
@Service
public class BookService {
private final BookRepository bookRepository;

public BookService(BookRepository bookRepository) {
this.bookRepository = bookRepository;
}

public List<Book> getAllBooks() {
return bookRepository.findAll();
}

public Book getBookById(Long id) {
return bookRepository.findById(id);
}

public void addBook(Book book) {
bookRepository.save(book);
}

public void updateBook(Long id, Book updatedBook) {
Book existingBook = bookRepository.findById(id);
if (existingBook != null) {
existingBook.setTitle(updatedBook.getTitle());
existingBook.setAuthor(updatedBook.getAuthor());
existingBook.setPrice(updatedBook.getPrice());
bookRepository.save(existingBook);
}
}

public void deleteBook(Long id) {
bookRepository.deleteById(id);
}
}
“`

In this example, the `BookService` class provides methods to retrieve all books, get a book by its ID, add a new book, update an existing book, and delete a book. The service class interacts with the `BookRepository` to perform database operations.

3. Implementing Controller Methods:

To expose the business logic as RESTful endpoints, we need to implement controller methods that communicate with the client. Let’s create a `BookController` class to handle book-related requests:

“`java
@RestController
@RequestMapping(“/books”)
public class BookController {
private final BookService bookService;

public BookController(BookService bookService) {
this.bookService = bookService;
}

@GetMapping
public List<Book> getAllBooks() {
return bookService.getAllBooks();
}

@GetMapping(“/{id}”)
public Book getBookById(@PathVariable Long id) {
return bookService.getBookById(id);
}

@PostMapping
public void addBook(@RequestBody Book book) {
bookService.addBook(book);
}

@PutMapping(“/{id}”)
public void updateBook(@PathVariable Long id, @RequestBody Book updatedBook) {
bookService.updateBook(id, updatedBook);
}

@DeleteMapping(“/{id}”)
public void deleteBook(@PathVariable Long id) {
bookService.deleteBook(id);
}
}
“`

In this example, the `BookController` class defines endpoints for retrieving all books, getting a book by its ID, adding a new book

, updating an existing book, and deleting a book. The controller methods delegate the actual operations to the `BookService` class.

4. Wiring Components with Dependency Injection:

To enable dependency injection and wire the components together, we need to configure the Spring context. We can use annotations such as `@Service` and `@Autowired` to let Spring handle the instantiation and injection of dependencies.

“`java
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
“`

In this example, the `@SpringBootApplication` annotation on the main class enables auto-configuration and component scanning. It also starts the Spring Boot application.

Conclusion:

Implementing business logic is a critical step in building a Spring Boot application. In this section, we explored the process of defining the domain model, creating service classes to encapsulate the business logic, implementing controller methods to expose the functionality as RESTful endpoints, and wiring the components together using dependency injection. By following the provided code samples and understanding the principles of building business logic in Spring Boot, you can create robust and scalable applications. In the next section, we will continue building our application by adding data persistence with Spring Data JPA.