Spring Boot Starters

What a Starter Actually Is — Two Things, Not One

The name "starter" suggests a single mechanism. It's actually two separate things working together, and conflating them is the source of most "why did adding this dependency change my app's behaviour" confusion:

Adding spring-boot-starter-web to your POM does two things at once: it pulls in spring-webmvc, spring-boot-starter-tomcat, jackson-databind, and a handful of others (the starter's job), and those JARs each ship @AutoConfiguration classes that Spring Boot discovers and conditionally activates (auto-configuration's job). The starter is the trigger; the auto-configuration is the actual behaviour change.

Common Starters and What They Actually Pull In

<!-- pom.xml — no <version> needed: spring-boot-starter-parent manages all versions -->
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

Excluding Auto-Configuration

Auto-configuration is conditional — every @AutoConfiguration class is gated by one or more @ConditionalOn* annotations (@ConditionalOnClass, @ConditionalOnMissingBean, etc.) and only activates when those conditions are met. Usually this means it stays out of your way — the moment you define your own DataSource bean, DataSourceAutoConfiguration backs off. Sometimes, though, you need to exclude it explicitly:

// Exclude at the application level — affects all contexts
@SpringBootApplication(exclude = {
    DataSourceAutoConfiguration.class,       // module that has no database
    SecurityAutoConfiguration.class           // internal tool with no login required
})
public class MyApp { ... }

// Or via properties — useful when you can't modify the main class

# application.properties
spring.autoconfigure.exclude=\
  org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
  org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration

Writing a Custom Starter

A custom starter is the right pattern when a cross-cutting concern — audit logging, a company-wide HTTP client configuration, a shared security policy — needs to be reused across multiple Spring Boot applications without each team re-implementing it. The structure follows the same two-part pattern as official starters:

/*
 * Recommended layout:
 *
 *   my-feature-spring-boot-starter/     ← empty POM, declares the autoconfigure module
 *   my-feature-spring-boot-autoconfigure/ ← the actual @AutoConfiguration class + conditions
 *
 * Naming convention: {feature}-spring-boot-starter
 * Official starters use spring-boot-starter-{feature} — the reversed form is reserved for
 * Spring's own starters; third-party and internal starters use your-name first.
 */

// 1. The auto-configuration class
@AutoConfiguration
@ConditionalOnClass(AuditService.class)          // only if the feature is on the classpath
@ConditionalOnMissingBean(AuditService.class)    // back off if the app defined its own
@EnableConfigurationProperties(AuditProperties.class)
public class AuditAutoConfiguration {

    @Bean
    public AuditService auditService(AuditProperties props) {
        return new DefaultAuditService(props);
    }
}

# 2. Register it for discovery
# src/main/resources/META-INF/spring/
#   org.springframework.boot.autoconfigure.AutoConfiguration.imports

com.example.audit.AuditAutoConfiguration

<!-- 3. The starter POM — no Java code, just dependency declarations -->
<dependencies>
    <dependency>
        <groupId>com.example</groupId>
        <artifactId>my-feature-spring-boot-autoconfigure</artifactId>
    </dependency>
    <!-- any other transitive dependencies the feature needs -->
</dependencies>

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