Mastering @Import in Spring: Dynamic Routes and Custom Bean Registration

Today I share the injection forms of @Import used in pig4cloud. Different injection methods help keep the architecture concise.

Importing a Component with @Import

The EnablePigxDynamicRoute annotation enables dynamic data sources; simply add it to the main method.

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(DynamicRouteAutoConfiguration.class)
public @interface EnablePigxDynamicRoute {
}

The core is importing the DynamicRouteAutoConfiguration class, which is not managed by Spring's component scan.

Simple example:

public class Dog {
}

@Import({Dog.class})
@SpringBootApplication
public class SpringLearnApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringLearnApplication.class, args);
        Assert.isTrue(context.containsBean("com.pig4cloud.spring.learn.demo1.Dog"), "error dog bean");
    }
}

Note that Dog does not have the declarative annotation; it is injected as a bean by its full class name.

ImportSelector Interface

When @Import references a class that implements ImportSelector, the selector determines which classes to import.

public class DogImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        // matching logic returns class names to import
        return new String[]{"com.pig4cloud.spring.learn.demo1.Dog"};
    }
}

@Import({DogImportSelector.class})
@SpringBootApplication
public class SpringLearnApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringLearnApplication.class, args);
        Assert.isTrue(context.containsBean("com.pig4cloud.spring.learn.demo1.Dog"), "error dog bean");
    }
}

ImportBeanDefinitionRegistrar

When @Import references a class that implements ImportBeanDefinitionRegistrar, the beans defined in registerBeanDefinitions are automatically registered.

Using pig's resource server configuration, it automatically registers a PigxResourceServerConfigurerAdapter bean named resourceServerConfigurerAdapter.

public class PigxSecurityBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(PigxResourceServerConfigurerAdapter.class);
        registry.registerBeanDefinition(SecurityConstants.RESOURCE_SERVER_CONFIGURER, beanDefinition);
    }
}

Thus, adding the EnablePigxResourceServer annotation enables pig4cloud's packaged OAuth resource client operations, serving as the entry point of the source code.

@Import({PigxSecurityBeanDefinitionRegistrar.class})
public @interface EnablePigxResourceServer {
}