How to Build Your Own Spring Boot Starter: A Step‑by‑Step Guide

Quick Start

Create a new Maven project. Name it xxx-spring-boot-starter, e.g., didispace-spring-boot-starter.

Edit pom.xml and add spring-boot-autoconfigure and spring-boot-starter dependencies.

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

Create Configuration Class

Define a class annotated with @Configuration and use @Bean, @ConditionalOnClass, @ConditionalOnMissingBean etc. to control bean creation.

@Configuration
@ConditionalOnClass(MyFeature.class)
@ConditionalOnProperty(prefix="myfeature", name="enabled", matchIfMissing=true)
public class MyFeatureAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public MyFeature myFeature() {
        return new MyFeature();
    }
}

Register Auto‑Configuration

Under src/main/resources/META-INF create spring.factories and list the auto‑configuration class:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.didispace.myfeature.MyFeatureAutoConfiguration

Note: Starting with Spring Boot 2.7, spring.factories is deprecated; use META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports instead.

Validation Testing

Write unit tests with @SpringBootTest to load the full application context and verify beans and properties.

@SpringBootTest(classes = TestApplication.class)
public class MyStarterAutoConfigurationTest {

    @Autowired(required = false)
    private MyService myService;

    @Test
    public void testMyServiceAutoConfigured() {
        assertNotNull(myService, "MyService should be auto-configured");
    }
}

Use @TestPropertySource or @DynamicPropertySource to override properties, or set them directly in @SpringBootTest:

@SpringBootTest(properties = "my.starter.custom-property=customValue")
public class MyStarterPropertiesTest {

    @Value("${my.starter.custom-property}")
    private String customProperty;

    @Test
    public void testPropertyOverride() {
        assertEquals("customValue", customProperty,
            "Custom property should be overridden by @SpringBootTest");
    }
}

For conditional configurations, add tests that cover each branch, optionally using @TestConfiguration to enable or disable specific auto‑configurations.

Conclusion

The article covered two advanced Spring Boot topics: creating a Spring Boot Starter and providing unit tests for it.