@Autowired for dependency injection in Spring Boot - Mini Project: Build & Apply

Using @Autowired for Dependency Injection in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that manages messages. You want to use Spring's dependency injection to automatically provide a service to your controller.

🎯 Goal: Learn how to use @Autowired to inject a service into a controller in Spring Boot.

📋 What You'll Learn

Create a service class called MessageService with a method getMessage() that returns a string.

Create a controller class called MessageController.

Use @Autowired to inject MessageService into MessageController.

Add a method in MessageController that calls getMessage() from the service.

💡 Why This Matters

🌍 Real World

Dependency injection with @Autowired is a common pattern in Spring Boot applications to manage components and their dependencies automatically.

💼 Career

Understanding @Autowired and dependency injection is essential for Java developers working with Spring Boot to build maintainable and testable applications.

1

Create the MessageService class

Create a class called MessageService annotated with @Service. Inside it, write a method public String getMessage() that returns the string "Hello from MessageService".

Spring Boot

// Your code here

Need a hint?

Use @Service to mark the class as a service component.

2

Create the MessageController class

Create a class called MessageController annotated with @RestController. This class will later use the service.

Spring Boot

import org.springframework.stereotype.Service;

@Service
public class MessageService {
    public String getMessage() {
        return "Hello from MessageService";
    }
}

// Your code here

Need a hint?

Use @RestController to mark the class as a controller that returns data.

3

Inject MessageService into MessageController using @Autowired

Inside MessageController, declare a private field messageService of type MessageService. Use @Autowired above it to inject the service.

Spring Boot

import org.springframework.stereotype.Service;

@Service
public class MessageService {
    public String getMessage() {
        return "Hello from MessageService";
    }
}

import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Autowired;

@RestController
public class MessageController {
    // Your code here
}

Need a hint?

Use @Autowired to let Spring inject the service automatically.

4

Add a method in MessageController to use the injected service

In MessageController, add a method public String showMessage() annotated with @GetMapping("/message"). This method should return the result of calling messageService.getMessage().

Spring Boot

import org.springframework.stereotype.Service;

@Service
public class MessageService {
    public String getMessage() {
        return "Hello from MessageService";
    }
}

import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;

@RestController
public class MessageController {
    @Autowired
    private MessageService messageService;

    // Your code here
}

Need a hint?

Use @GetMapping to create a web endpoint that returns the message.