Multi-tiered Spring application dependency resolution

Question

I am trying to create a three-tier application with Spring, view , logic , data , more or less. The view depends on logic which depends on data .

How can I configure the Spring application in the view project such that the dependency graph is able to be resolved?

For example:

In the view layer:

@Controller
public class SomeView {
  private final SomeService someService;

  @Autowired
  public SomeView(SomeService someService) {
    this.someService = someService;
  }
}

@Configuration
@EnableAutoConfiguration
@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

In the logic layer:

@Component
public class SomeService {

  private final SomeData someData;

  @Autowired
  public SomeService(SomeData someData){
    this.someData = someData;
  }

}

In the data layer:

@Component
public class SomeData {

}

This configuration is not able to boot because SomeService can't resolve SomeData because SomeData is not scanned in the view layers Application.java

Answer 1

when using @SpringBootApplication Spring boot uses default values. If you take a look at the @SpringBootApplication definition you will see that :

Many Spring Boot developers always have their main class annotated with @Configuration, @EnableAutoConfiguration and @ComponentScan. Since these annotations are so frequently used together (especially if you follow the best practices above), Spring Boot provides a convenient @SpringBootApplication alternative.

The @SpringBootApplication annotation is equivalent to using @Configuration, @EnableAutoConfiguration and @ComponentScan with their default attributes: [...]

That means :

@SpringBootApplication // same as @Configuration    @EnableAutoConfiguration @ComponentScan
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

Also, it means that when using default values for @ComponentScan your packages sturctures shloud be as following :

• com.example.model -> your entities
• com.example.repositoriy -> your repositories
• com.example.controller -> controllers
• com.example -> MainApplication class

If not following this structure you should tell to the @ComponentScan the package where to find the components :

Example 1:

@Configuration
@EnableAutoConfiguration
@ComponentScan({"com.my.package.controller","com.my.package.domain"})
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

Exemple 2 :

    @Configuration
@EnableAutoConfiguration
@ComponentScan(basePackageClasses = {SomeService.class, SomeData.class})
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

Also, i advice you to check this guide on how to structuring your code in a Spring Boot Application.