Bean lifecycle overview in Spring Boot - Mini Project: Build & Apply

Bean lifecycle overview

📖 Scenario: You are building a simple Spring Boot application that manages a bean representing a user service. You want to understand how Spring creates, initializes, and destroys beans during the application lifecycle.

🎯 Goal: Create a Spring Boot bean called UserService and demonstrate the bean lifecycle by adding initialization and destruction methods.

📋 What You'll Learn

Create a bean class named UserService

Add a method annotated with @PostConstruct for initialization

Add a method annotated with @PreDestroy for cleanup

Configure the bean in the Spring context using @Component

Create a main Spring Boot application class to run the context

💡 Why This Matters

🌍 Real World

Understanding bean lifecycle helps you manage resources like database connections or caches properly in real Spring applications.

💼 Career

Spring Boot is widely used in enterprise Java development; knowing bean lifecycle is essential for building robust and maintainable applications.

1

Create the UserService bean class

Create a class named UserService in package com.example.demo and annotate it with @Component.

Spring Boot

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

Need a hint?

Use @Component to tell Spring this is a bean.

2

Add initialization method with @PostConstruct

Inside UserService, add a method named init annotated with @PostConstruct that prints "UserService initialized".

Spring Boot

package com.example.demo;

import org.springframework.stereotype.Component;
import jakarta.annotation.PostConstruct;

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

Need a hint?

Use @PostConstruct to run code after bean creation.

3

Add destruction method with @PreDestroy

Inside UserService, add a method named cleanup annotated with @PreDestroy that prints "UserService destroyed".

Spring Boot

package com.example.demo;

import org.springframework.stereotype.Component;
import jakarta.annotation.PostConstruct;
import jakarta.annotation.PreDestroy;

@Component
public class UserService {
    @PostConstruct
    public void init() {
        System.out.println("UserService initialized");
    }
    // Your code here
}

Need a hint?

Use @PreDestroy to run code before bean destruction.

4

Create main Spring Boot application class

Create a class named DemoApplication in package com.example.demo with @SpringBootApplication annotation and a main method that runs SpringApplication.run(DemoApplication.class, args).

Spring Boot

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
    // Your code here
}

Need a hint?

This class starts the Spring Boot application.