How to Build and Use a Custom Spring Boot Starter in Minutes

In Spring Boot we often see Maven coordinates like spring-boot-starter-web . Spring Boot extracts common scenarios into "starters" that can be added with minimal configuration to obtain the desired functionality.

Enterprises may wrap internal middleware as a starter so other projects can depend on it and get automatic configuration. The following guide shows how to create a custom starter.

1. Custom Starter

Requirement: Use a custom starter to provide configurable parameters for each project and read those values.

The project structure is illustrated below:

(1) Add necessary dependencies in the custom starter module:

<code>&lt;dependencies&gt;
    &lt;dependency&gt;
        &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
        &lt;artifactId&gt;spring-boot-autoconfigure&lt;/artifactId&gt;
    &lt;/dependency&gt;
    
    &lt;dependency&gt;
        &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
        &lt;artifactId&gt;spring-boot-autoconfigure-processor&lt;/artifactId&gt;
    &lt;/dependency&gt;
    
    &lt;dependency&gt;
        &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
        &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
    &lt;/dependency&gt;
&lt;/dependencies&gt;</code>

(2) Create a configuration class to read custom properties:

<code>@Component
@ConfigurationProperties("com.longxia")
@Data
public class MytConfigProperty {
    private String name;
    private Integer age;
}</code>

(3) Define a service that uses the configuration:

<code>public class MyService {
    private MyConfigProperty myConfigProperty;

    public MyService() {}

    public MyService(MytConfigProperty myConfigProperty) {
        this.myConfigProperty = myConfigProperty;
    }

    public String say() {
        return "myStarter " + myConfigProperty.getName() + " !";
    }
}</code>

(4) Add service configuration:

<code>@Configuration
@EnableConfigurationProperties({MytConfigProperty.class})
public class MyConfig {
    @Resource
    private MyConfigProperty myConfigProperty;

    @Bean
    public MyFirstService getMyFirstService() {
        return new MyFirstService(myFirstConfigProperty);
    }
}</code>

(5) Write spring.factories to make the starter discoverable:

<code>org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.longxia.spring.starter.config.MyConfig</code>

The purpose of spring.factories is to let Spring Boot scan and load the custom starter during application startup.

2. Use the Custom Starter

(1) Add the custom starter as a Maven dependency:

<code>&lt;dependency&gt;
    &lt;groupId&gt;com.longxia.cloud&lt;/groupId&gt;
    &lt;artifactId&gt;common-starter&lt;/artifactId&gt;
    &lt;version&gt;1.0-SNAPSHOT&lt;/version&gt;
&lt;/dependency&gt;</code>

(2) Add configuration property values in the consuming project's configuration file (example shown below):

(3) Define a controller to test the starter:

<code>@RestController
@RequestMapping("/starter")
public class MyFirstStarterController {
    @Resource
    private MytService myService;

    @GetMapping("/first")
    public String first() {
        return mytService.hello();
    }
}</code>

Access the endpoint in a browser at http://localhost:8080/starter/first and you will see the response, as shown in the screenshot below:

With these steps, the custom starter is complete. Any business module that needs the encapsulated common-starter can simply add its Maven dependency and the corresponding configuration to start using it.