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

Quick Start

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

Edit pom.xml and add the 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 a configuration class annotated with @Configuration. Inside, define beans using @Bean and control their loading with conditional annotations such as @ConditionalOnClass and @ConditionalOnMissingBean.

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

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

Under src/main/resources/META-INF, create a spring.factories file and list your auto‑configuration class under the

org.springframework.boot.autoconfigure.EnableAutoConfiguration

key.

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, listing the fully‑qualified class names of auto‑configuration classes.

Validation Tests

When building a Spring Boot Starter, always write unit tests to verify that the auto‑configuration behaves as expected under various conditions.

Create Unit Tests

Use @SpringBootTest to load the full application context and assert that beans and properties are correctly configured.

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

    @Autowired(required = false)
    private MyService myService;

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

Override Different Configurations

Use @TestPropertySource or @DynamicPropertySource to supply alternative property values, or set properties directly on @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");
    }
}

Test Conditional Branches

If your starter contains conditional annotations like @ConditionalOnProperty or @ConditionalOnClass, write tests that cover each branch.

@SpringBootTest(classes = {TestApplication.class, MyConditionalConfiguration.class})
@ConditionalOnProperty(name = "my.starter.enable", havingValue = "true")
public class MyStarterConditionalTest {

    @Autowired
    private ApplicationContext context;

    @Test
    public void conditionalBeanNotLoadedWhenPropertyIsFalse() {
        assertFalse(context.containsBean("conditionalBean"), "Conditional bean should not be loaded when 'my.starter.enable' is false");
    }
}

Use @TestConfiguration to selectively enable or disable auto‑configuration classes during testing.

Summary

The article covered two advanced Spring Boot topics: how to create a Spring Boot Starter and how to provide comprehensive unit tests for it. Mastering these skills enables you to package reusable modules and ensure they work reliably in any Spring Boot application.