Bean concept in Spring in Spring Boot - Mini Project: Build & Apply

Understanding the Bean Concept in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that manages a greeting message. You want to understand how Spring manages objects called beans to reuse them easily across your app.

🎯 Goal: Create a Spring Boot application that defines a bean for a greeting message, configures it, uses it in a service, and finally injects it into a controller to display the greeting.

📋 What You'll Learn

Create a configuration class with a bean method returning a greeting string

Add a configuration variable to customize the greeting message

Use the bean in a service class to provide the greeting

Inject the service into a controller and return the greeting from an endpoint

💡 Why This Matters

🌍 Real World

Spring beans are the foundation of managing objects in Spring applications. This project shows how to create and use beans to share data and logic easily.

💼 Career

Understanding Spring beans is essential for Java developers working with Spring Boot, as it enables clean, modular, and testable code.

1

Create a configuration class with a bean

Create a class called GreetingConfig annotated with @Configuration. Inside it, write a method called greetingMessage annotated with @Bean that returns the string "Hello, Spring!".

Spring Boot

@Configuration
public class GreetingConfig {
    // Your code here
}

Need a hint?

Use @Configuration on the class and @Bean on the method that returns the greeting string.

2

Add a configuration variable for the greeting

Inside the GreetingConfig class, add a private final string variable called customGreeting initialized to "Welcome to Spring Boot!". Change the greetingMessage method to return customGreeting instead of the fixed string.

Spring Boot

@Configuration
public class GreetingConfig {
    // Add a private final String customGreeting initialized to "Welcome to Spring Boot!"

    @Bean
    public String greetingMessage() {
        // Return customGreeting here
    }
}

Need a hint?

Define a private final variable and return it from the bean method.

3

Create a service class that uses the greeting bean

Create a class called GreetingService annotated with @Service. Add a private final string field called message. Use constructor injection with @Autowired to receive the greetingMessage bean and assign it to message. Add a method getGreeting() that returns message.

Spring Boot

@Service
public class GreetingService {
    private final String message;

    // Add constructor with @Autowired to inject greetingMessage bean

    public String getGreeting() {
        // Return the message field
    }
}

Need a hint?

Use constructor injection with @Autowired to get the bean and store it in a field.

4

Inject the service into a controller and return the greeting

Create a class called GreetingController annotated with @RestController. Inject GreetingService using constructor injection. Add a @GetMapping("/greet") method called greet() that returns the result of getGreeting() from the service.

Spring Boot

@RestController
public class GreetingController {
    private final GreetingService greetingService;

    // Add constructor to inject GreetingService

    @GetMapping("/greet")
    public String greet() {
        // Return greetingService.getGreeting()
    }
}

Need a hint?

Use constructor injection to get the service and return its greeting in the controller method.