Spring Boot Starter Modules Explained | Auto-Configuration Guide

🚀 Introduction to Spring Boot Starter Modules

Spring Boot Starter Modules are pre-configured dependency packages that help developers quickly integrate features without manually configuring each library.

✅ Why Use Spring Boot Starter Modules?
✔ Simplifies Dependency Management – No need to add multiple dependencies manually.
✔ Enables Auto-Configuration – Automatically configures beans based on the starter module.
✔ Reduces Boilerplate Code – Saves time by handling default configurations.
✔ Improves Maintainability – Ensures consistent setup across different projects.

📌 In this guide, you’ll learn:
✅ What Spring Boot Starters are and how they work.
✅ Common Spring Boot Starter modules and their usage.
✅ How to customize auto-configuration in starters.

1️⃣ What Are Spring Boot Starter Modules?

A Spring Boot Starter is a dependency bundle that includes multiple related libraries and auto-configuration settings.

🔹 Example Without Starter Modules (Manual Dependencies)

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
</dependency>

🚀 Instead of adding each dependency manually, we can use a Starter Module!

🔹 Example With a Starter Module (Simplified Approach)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

✅ This single dependency automatically includes all required libraries for building a web application!

2️⃣ List of Common Spring Boot Starter Modules

Below is a list of the most commonly used Spring Boot Starter Modules with their descriptions:

Spring Boot Starter	Description
spring-boot-starter-web	Starter for building web applications using Spring MVC with Tomcat as default.
spring-boot-starter-data-jpa	Starter for using Spring Data JPA with Hibernate as the default ORM.
spring-boot-starter-security	Starter for securing Spring Boot applications with Spring Security.
spring-boot-starter-test	Starter for testing Spring Boot applications with JUnit, Mockito, and AssertJ.
spring-boot-starter-thymeleaf	Starter for integrating Thymeleaf template engine for server-side rendering.
spring-boot-starter-actuator	Starter for adding Actuator endpoints for monitoring and metrics.
spring-boot-starter-data-mongodb	Starter for using MongoDB NoSQL database with Spring Data MongoDB.
spring-boot-starter-data-redis	Starter for using Redis as a cache or message broker in Spring applications.
spring-boot-starter-mail	Starter for sending emails using JavaMailSender API.
spring-boot-starter-amqp	Starter for messaging with RabbitMQ using Spring AMQP.
spring-boot-starter-batch	Starter for batch processing with Spring Batch.
spring-boot-starter-cache	Starter for caching with abstraction over various caching implementations.
spring-boot-starter-validation	Starter for validation using Java Bean Validation API.
spring-boot-starter-oauth2-client	Starter for implementing OAuth2 authentication and authorization.
spring-boot-starter-cloud-connectors	Starter for integrating cloud connectors for cloud-based applications.
spring-boot-starter-quartz	Starter for job scheduling using Quartz Scheduler.
spring-boot-starter-webflux	Starter for building reactive web applications using Spring WebFlux.
spring-boot-starter-aop	Starter for Aspect-Oriented Programming (AOP) using Spring AOP.
spring-boot-starter-integration	Starter for Spring Integration framework for messaging-based applications.
spring-boot-starter-jdbc	Starter for traditional JDBC database access with HikariCP as default connection pool.

 Understanding Different Spring Boot Starter Modules

1️⃣ spring-boot-starter-web (For Web Applications)

📌 Adds support for:
✔ Spring MVC
✔ Embedded Tomcat, Jetty, or Undertow
✔ Jackson (JSON processing)

📌 Example Usage

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

📌 Example REST API Controller

@RestController
@RequestMapping("/api")
public class DemoController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, Spring Boot!";
    }
}

✅ Auto-configures an embedded web server and REST API capabilities.

2️⃣ spring-boot-starter-data-jpa (For Database Access with JPA & Hibernate)

📌 Adds support for:
✔ Spring Data JPA
✔ Hibernate ORM
✔ Database connection pooling (HikariCP)

📌 Example Usage

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

📌 Example JPA Entity & Repository

@Entity
public class Product {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    private double price;
}

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
}

✅ Auto-configures JPA and Hibernate for database operations.

3️⃣ spring-boot-starter-security (For Authentication & Authorization)

📌 Adds support for:
✔ Spring Security framework
✔ Default user authentication
✔ Password encryption

📌 Example Usage

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

📌 Default Behavior:

• By default, Spring Security enables basic authentication with a generated password.
• The password is printed in logs on startup:

Using generated security password: 1234abcd-5678-efgh-ijkl

📌 Custom Security Configuration

@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/admin/**").authenticated()
                .anyRequest().permitAll()
            )
            .formLogin()
            .httpBasic();
        return http.build();
    }
}

✅ Auto-configures authentication and login security.

4️⃣ spring-boot-starter-test (For Unit & Integration Testing)

📌 Adds support for:
✔ JUnit 5
✔ Mockito (Mocking framework)
✔ Spring Test

📌 Example Usage

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>

📌 Example Unit Test

@SpringBootTest
public class ProductServiceTest {

    @Autowired
    private ProductService productService;

    @Test
    public void testGetAllProducts() {
        List<Product> products = productService.getAllProducts();
        assertNotNull(products);
    }
}

✅ Auto-configures a testing framework with necessary dependencies.

4️⃣ How to Disable Auto-Configuration in Starter Modules?

Spring Boot automatically configures beans, but you can disable unwanted auto-configurations.

📌 Method 1: Use exclude in @SpringBootApplication

@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class })
public class MyApplication { }

📌 Method 2: Use spring.autoconfigure.exclude in application.properties

spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

✅ This prevents Spring Boot from configuring unwanted beans.

🎯 Summary: What We Learned

✅ Spring Boot Starters simplify dependency management.
✅ Each Starter Module provides auto-configuration for a specific feature.
✅ Common Spring Boot Starters: Web, Data JPA, Security, Test, etc.
✅ You can disable unwanted auto-configurations when necessary.

🚀 Using Starter Modules makes Spring Boot development faster and cleaner!