@Component annotation in Spring Boot - Mini Project: Build & Apply

Using @Component Annotation in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that manages a greeting service. You want to create a reusable component that provides a greeting message.

🎯 Goal: Create a Spring Boot component using the @Component annotation and use it in the main application to display a greeting message.

📋 What You'll Learn

Create a class annotated with @Component

Define a method that returns a greeting string

Inject the component into the main application class

Call the greeting method and store the result in a variable

💡 Why This Matters

🌍 Real World

Spring Boot components are used to organize reusable parts of an application, like services or helpers, that can be injected where needed.

💼 Career

Understanding <code>@Component</code> and dependency injection is essential for building maintainable and testable Spring Boot applications, a common skill in Java backend development jobs.

1

Create a Greeting Component Class

Create a class called GreetingService and annotate it with @Component. Inside the class, create a method called getGreeting that returns the string "Hello, Spring!".

Spring Boot

@Component
public class GreetingService {
    // Your code here
}

Need a hint?

Use @Component above the class declaration to make it a Spring component.

2

Add a Field to Inject GreetingService

In the main application class called Application, add a private field of type GreetingService annotated with @Autowired to inject the component.

Spring Boot

@Component
public class GreetingService {
    public String getGreeting() {
        return "Hello, Spring!";
    }
}

public class Application {
    @Autowired
    private GreetingService greetingService;
    // Your code here
}

Need a hint?

Use @Autowired to let Spring inject the GreetingService instance.

3

Call the Greeting Method

Inside the Application class, create a method called run that calls greetingService.getGreeting() and stores the result in a variable called message.

Spring Boot

@Component
public class GreetingService {
    public String getGreeting() {
        return "Hello, Spring!";
    }
}

public class Application {
    @Autowired
    private GreetingService greetingService;

    public void run() {
        // Your code here
    }
}

Need a hint?

Call the method on the injected greetingService and save the result in message.

4

Add @SpringBootApplication and Run Method Call

Annotate the Application class with @SpringBootApplication. Inside the main method, create an ApplicationContext and get the Application bean. Then call the run method on it.

Spring Boot

@Component
public class GreetingService {
    public String getGreeting() {
        return "Hello, Spring!";
    }
}

@SpringBootApplication
public class Application {
    @Autowired
    private GreetingService greetingService;

    public void run() {
        String message = greetingService.getGreeting();
    }

    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

Use SpringApplication.run to start the app and get the Application bean from the context.