Use @PostConstruct annotation to manage instance after creation

This project is based on chapter 2.2.2. Using stereotype annotations to add beans to the Spring context from book Spring Starts here (2021) by Laurentiu Spilca.

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 entity

@Component
public class Book {
    private String title;

    public Book() {
        this.title = "One Hundred Years of Solitude";
    }

    public String getTitle() {
        return title;
    }
}

Add Jakarta Annotations API dependency

<dependency>
    <groupId>jakarta.annotation</groupId>
    <artifactId>jakarta.annotation-api</artifactId>
    <version>3.0.0</version>
</dependency>

Add post-construct method to entity

@Component
public class Book {
    private String title;

    public Book() {
        this.title = "One Hundred Years of Solitude";
    }

+   @PostConstruct
+   public void init() {
+       this.title = "Changed title";
+   }

    public String getTitle() {
        return title;
    }
}

Create configuration class

@Configuration
@ComponentScan(basePackages = "org.example")
public class ApplicationConfiguration {
}

Create Spring context

ApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);

Get bean from Spring context

Book book = context.getBean(Book.class);
System.out.println("The book's title is " + book.getTitle());

Add tests

Add dependency for Spring TestContext Framework

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

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 to check that application context is created

public class ApplicationTests {

    @Test
    @DisplayName("Checks that Application Context is created")
    public void checkApplicationContextCreated() {
        ApplicationContext context = new AnnotationConfigApplicationContext();

        assertNotNull(context);
    }
}

Create test to check that book title was changed after bean creation

• use @ExtendWith(SpringExtension.class) to integrate Spring TestContext Framework to the test
• use @ContextConfiguration to configure Spring context in Spring integration tests

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = { ApplicationConfiguration.class })
public class BookTests {

    @Autowired
    private Book book;

    @Test
    @DisplayName("Check that the book title was changed")
    public void checkBookTitleChanged() {
        String actualTitle = book.getTitle();

        String expectedTitle = "Changed title";

        assertEquals(expectedTitle, actualTitle);
    }
}