Using @Import for Modular Spring Boot Development and Dynamic Bean Registration

When developing Spring Boot back‑end applications, a four‑layer architecture can become cumbersome as the project grows, leading to many xxxDAO and xxxService classes.

To keep the codebase manageable, the article suggests splitting a monolithic project into multiple Maven modules and using @Import to bring the beans of each module into the main application context without converting to a distributed micro‑service architecture.

1. Using @ComponentScan

The article reviews how @SpringBootApplication includes @ComponentScan and how specifying scanBasePackages changes the scanning base.

package com.gitee.swsk33.mainmodule;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

2. Basic use of @Import

By annotating a configuration class with @Import(DemoFunction.class) , the specified class is also registered as a bean.

@Configuration
@Import(DemoFunction.class)
public class FunctionImportConfig {}

3. Encapsulating @Import in a custom annotation

A custom annotation such as @EnableFunctionOne can be created to import a module’s scanning entry point.

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(FunctionOneApplication.class)
public @interface EnableFunctionOne {}

4. Dynamic import with ImportSelector

Implementing ImportSelector allows runtime selection of classes to import.

public class DemoImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        System.out.println("Importing class: " + importingClassMetadata.getClassName());
        return new String[]{"com.gitee.swsk33.functionone.FunctionOneApplication",
                         "com.gitee.swsk33.functiontwo.FunctionTwoApplication"};
    }
}

5. Dynamic import with ImportBeanDefinitionRegistrar

By implementing ImportBeanDefinitionRegistrar , beans can be registered programmatically.

public class DemoImportRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        GenericBeanDefinition bean1 = new GenericBeanDefinition();
        bean1.setBeanClass(FunctionOneApplication.class);
        registry.registerBeanDefinition("functionOneComponentScan", bean1);
        // similarly for FunctionTwoApplication
    }
}

6. Conditional import

Using @ConditionalOnProperty on the configuration class can enable or disable the import based on application properties.

@Configuration
@Import(FunctionOneApplication.class)
@ConditionalOnProperty(prefix="com.gitee.swsk33.function-one", name="enabled")
public class FunctionImportConfig {}

The article concludes that @Import is a powerful tool for Spring Boot modular development, allowing both static and dynamic inclusion of configuration classes and scanning entry points.