Hands-On: Building a Custom Spring Boot Starter with Gradle

We’ll create a Spring Boot starter for a “Custom Logging Service”, which can be reused across multiple projects. This service will log incoming requests with a custom header.

https://youtube.com/@codefarm0

Step 1: Set Up the Spring Boot Starter Project

1.1. Create a New Project

Use the Spring Initializr or manually create a Gradle project. Include the following dependencies:

• spring-boot-starter
• spring-boot-starter-web

Gradle Build File:

plugins {
    id 'java'
    id 'org.springframework.boot' version '3.4.0'
    id 'io.spring.dependency-management' version '1.1.3'
    id 'maven-publish'
}
group = 'com.codefarm'
version = '0.0.1-SNAPSHOT'
java {
    sourceCompatibility = JavaVersion.VERSION_21
}
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

Step 2: Implement the Logging Service

2.1. Create a Filter for Custom Logging

Add a filter that logs incoming requests.

@WebFilter("/*")
@Component
public class LoggingUtilFilter implements Filter {

    private final Logger logger = LoggerFactory.getLogger(LoggingUtilFilter.class);
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
       HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        logger.info("Endpoint Called - : {} {}", httpServletRequest.getMethod(), httpServletRequest.getRequestURI());
        chain.doFilter(request, response);
    }
}

2.2. Add a Configuration Class

This will enable the logging feature conditionally.

@Configuration
@ConditionalOnProperty(name = "custom.logging.enabled", havingValue = "true", matchIfMissing = true)
public class LoggingAutoConfig {

    private Logger logger = LoggerFactory.getLogger(LoggingAutoConfig.class);
    @Bean
    LoggingUtilFilter loggingFilter(){
        logger.debug("Instantiating LoggingFilter");
        return new LoggingUtilFilter();
    }

}

Step 3: Register the Auto-Configuration

3.1. Add the autoconfig file details

Add a File: META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

com.codefarm.logging.config.LoggingAutoConfig

Note — Before Spring 3.x below was the way to do this

File: META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.codefarm.logging.config.LoggingAutoConfig

Step 4: Publish the Starter

4.1. Configure Gradle for Publishing

Add the following to your build.gradle file to publish the JAR file to a local or remote repository:

publishing {
 publications {
  mavenJava(MavenPublication) {
   from components.java
   versionMapping {
    usage('java-api') {
     fromResolutionOf('runtimeClasspath')
    }
    usage('java-runtime') {
     fromResolutionResult()
    }
   }
  }
 }
 repositories {
  maven {
   url = layout.buildDirectory.dir("local-maven-repo")
  }
 }
}

Run the following command to publish the starter locally:

./gradlew publish

The starter JAR will be available in the build/local-maven-repo directory.

Step 5: Use the Starter in Another Project

5.1. Add the Starter Dependency

Include the published starter in a new project:

Build File: build.gradle

dependencies {
    implementation 'com.codefarm:logging:0.0.1-SNAPSHOT'
}

To pull the starter from the local directory add the below code too in build.gradle

repositories {
    mavenCentral()
    maven{
       url = uri("file://E:\\codefarm\\SpringBoot\\custom-starter\\logging-starter\\build\\local-maven-repo")
    }
}

5.2. Enable Custom Logging

In application.properties:

custom.logging.enabled=true

Step 6: Test the Application

1. Start the application.
2. Send a request to any endpoint (e.g., GET /hello).
3. Verify that the custom log message (Endpoint called ………) appears in the console.

This example demonstrates how to create and reuse a custom Spring Boot starter.

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Here is the video on Youtube channel #codefarm to demo this which you should checkout