Wiring beans in the configuration file

This project is based on chapter 3.1. Implementing relationships among beans defined in the configuration file from book Spring Starts here (2021) by Laurentiu Spilca.

Class diagram

Create Maven project with Intellij Idea

File > New project > Java

Add Spring Context dependency

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>6.1.10</version>
</dependency>

Create entities

public class Book {
    private final String title;
    private final Author author;

    public Book(String title, Author author) {
        this.title = title;
        this.author = author;
    }

    public String getTitle() {
        return title;
    }

    public Author getAuthor() {
        return author;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Book book = (Book) obj;
        return title.equals(book.title) && author.equals(book.author);
    }

    @Override
    public int hashCode() {
        return title.hashCode() + author.hashCode();
    }
}

public class Author {
    private String name;

    public Author(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Author author = (Author) obj;
        return name.equals(author.name);
    }

    @Override
    public int hashCode() {
        return name.hashCode();
    }
}

Create repositories

public class AuthorRepository {
    public Author getAuthor() {
        return new Author("F. Scott Fitzgerald");
    }
}

public class BookRepository {
    public Book getBook(Author author) {
        return new Book("The Great Gatsby", author);
    }
}

Create service

public class BookService {
    private final BookRepository bookRepository;
    private final AuthorRepository authorRepository;

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

    public Book getBook() {
        final Author author = authorRepository.getAuthor();
        return bookRepository.getBook(author);
    }
}

Create configuration class

• BookRepository is wired to BookService using bookRepository() method call
• AuthorRepository is wired to BookService using authorRepository parameter

@Configuration
public class ApplicationConfiguration {
    @Bean
    public BookRepository bookRepository() {
        return new BookRepository();
    }

    @Bean
    public AuthorRepository authorRepository() {
        return new AuthorRepository();
    }

    @Bean
    public BookService bookService(AuthorRepository authorRepository) {
        return new BookService(bookRepository(), authorRepository);
    }
}

Create Spring context

ApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);

Get bean from Spring context

Book book = context.getBean(BookService.class).getBook();
System.out.println("The book is: " + book.getTitle() + " by " + book.getAuthor().getName());

Create Tests

Create unit tests for repositories

• AuthorRepository
• BookRepository

Add dependency for JUnit

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>5.11.0-M2</version>
    <scope>test</scope>
</dependency>

Create test

• use annotations @Test and @DisplayName to mark test methods
• use assertEquals method to compare expected and actual values

class AuthorRepositoryTest {

    @Test
    @DisplayName("Fetches the author")
    void getAuthor() {
        AuthorRepository authorRepository = new AuthorRepository();

        Author actual = authorRepository.getAuthor();
        Author expected = new Author("F. Scott Fitzgerald");

        assertEquals(expected, actual);
    }
}

Create unit test for service with mocked repositories

Add dependency for Mockito framework

• allows creating mock objects

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-core</artifactId>
    <version>5.12.0</version>
    <scope>test</scope>
</dependency>

Add dependency for Mockito JUnit 5 support

• allows to initialize mocks in JUnit 5 tests

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-junit-jupiter</artifactId>
    <version>5.12.0</version>
    <scope>test</scope>
</dependency>

Create test

• use @ExtendWith(MockitoExtension.class) annotation to add Mockito JUnit 5 support
• use @Mock annotation to mark fields that should be mocked

@ExtendWith(MockitoExtension.class)
class BookServiceTest {
    @Mock
    private BookRepository bookRepository;

    @Mock
    private AuthorRepository authorRepository;

    @Test
    @DisplayName("Combines the author and book to get the book")
    void getBook() {
        given(authorRepository.getAuthor()).willReturn(new Author("author"));
        given(bookRepository.getBook(new Author("author"))).willReturn(new Book("book", new Author("author")));

        BookService bookService = new BookService(bookRepository, authorRepository);

        Book actual = bookService.getBook();
        Book expected = new Book("book", new Author("author"));

        assertEquals(expected, actual);
    }
}

Create integration test

Add dependency for Spring TestContext Framework

Spring TestContext Framework provides support for loading Spring ApplicationContext and beans in tests.

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-test</artifactId>
    <version>6.1.10</version>
    <scope>test</scope>
</dependency>

Create test

• use @ExtendWith(SpringExtension.class) annotation to add Spring TestContext Framework support
• use @ContextConfiguration annotation to specify the configuration class

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = ApplicationConfiguration.class)
public class IntegrationTest {
    @Autowired
    private BookService bookService;

    @Test
    void fetchesBook() {
        Book actual = bookService.getBook();
        Book expected = new Book("The Great Gatsby", new Author("F. Scott Fitzgerald"));

        assertEquals(expected, actual);
    }
}