Spring Boot自动配置

Question

In my use case I have 2 projects say projectA and projectB projectB is added as maven dependency in projectA. From projectA I am trying to call projectB services. For that I have created a config class in projectB :

@Configuration
public class BeanConfig {

    @Bean
    @ConditionalOnMissingBean
    public MyService<String, Object> myBean(){
        return new MyServiceImpl();
    }
}

and in MyServiceImpl I am autowiring MyDao. Error is it is not able to create a bean for MyDao.

In case if I am mentioning below in projectA main class.

@SpringBootApplication(scanBasePackages = { "org.my.service" }) 

Everything runs fine.

How can I create Bean without mentioning base package in project A.

Answer 1

You are instantiating the MyServiceImpl

return new MyServiceImpl();

So Spring can't autowire anything in this class.

This has nothing to do with your multi module project.

Either you use Autowiring or you have to set the DAO on the service class in the configuration method.

Answer 2

If you want to scan individual beans without enabling component scan for entire package you can use:

@Import(MyServiceImpl.class)

Then this particular bean will be spring enabled and scanned for appropriate spring annotations.

UPDATED: As the other have already pointed out when you create your service through

return new MyServiceImpl();

This type of creation will dissable the autowiring capabilities for the MyServiceImpl. The reason for this is that once you call the constructor yourself Spring no longer participates in the creation of the bean and its dependencies.

The mechanism I have pointed you out through @Import declaration presumes that you have not enabled component scanning for your projectB from projectA. In that case if we asume that BeanConfig resides in projectA. Then you need to ensure 2 things:

1.Your repository in projectB should be annotated with @Repository, as your MyServiceImpl should be annotated with @Service 2.In your BeanConfig on a class level you should place the following definitions:

@Configuration
@Import({MyServiceImpl.class, MyDao.class})
public class BeanConfig {


}

Since MyServiceImpl and MyDao are annotated with Service and Repository, you will no longer need the annotated with @Bean method myBean.

For the @Repository annotation in projectB to work you need to have Repositories enabled at projectA. Make sure that you have it enabled through EnableJpaRepositories either by importing relevant class from projectB containing this annotation, or by annotating a Config class in projectA.

Answer 3

If you have your spring boot application structured properly, then you should not have to specify a base package to pick up your configuration. Spring boot should naturally scan the package containing your configuration and register your beans accordingly.

Reference: https://docs.spring.io/spring-boot/docs/current/reference/html/using-boot-structuring-your-code.html