Spring's annotations @ComponentScanand @ImportResourceto let Spring scan our custom annotations.
First, define a custom annotation AnimalType for marking cats and dogs:
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface AnimalType {
String value();
}
Next, define the cat and dog classes and mark them with the @AnimalType annotation:
@AnimalType("cat")
public class Cat {
// ...
}
@AnimalType("dog")
public class Dog {
// ...
}
Then, scan the package path through @ComponentScan in Spring's configuration class, so that it can scan our custom annotations:
@Configuration
@ComponentScan(basePackages = "com.example.animals")
public class AppConfig {
// ...
}
Finally, start the Spring container to get all classes marked with @AnimalType:
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
Map<String, Object> animalMap = context.getBeansWithAnnotation(AnimalType.class);
for (Object animal : animalMap.values()) {
System.out.println(animal.getClass().getSimpleName() + ": " + ((AnimalType)animal.getClass().getAnnotation(AnimalType.class)).value());
}
}
The output is:
Cat: cat
Dog: dog