AspectJ annotation of @DeclareParents add a new method to target

  　　　As we all know, AspectJ can be enhanced through connection points @ Before, @ After, @ Around such as annotation, today we play a new comment @DeclareParents. A new method for enhancing the target object.

• Scene introduction:

　　　　Now we have a class of animal duck, which has a function to swim, but suddenly one day we need to implement a delicious ingredients attribute to animals ducks. We can certainly go duck animal class to add a method, but contrary to the single principle. We can achieve enhanced by AOP.

• Code show time

　　There is a Animal interface

public interface Animal {

    void swim();
}

　　One more animal duck implementation class

@Repository ( "Animal" )
 public  class DuckAnimal the implements Animal { 
    @Override 
    public  void Swim () { 
        System.out.println ( "duck ... like to swim" ); 
    } 
}

　　Require an enhanced method to achieve a duck is a delicious food

public  interface Food {
     void EAT (); 
} 

@Repository ( "Food" )
 public  class DuckFood the implements Food { 
    @Override 
    public  void EAT () { 
        System.out.println ( "duck look tasty ..." ); 
    } 
}

　　Automatic injection

@ComponentScan("com.zjt.springboot.DeclareParents")
@Configuration
@EnableAspectJAutoProxy
public class AppConfiguration {
}

　　Declaring an aspect

@Aspect 
@Component 
public  class MyAspect { 

    / ** 
     * com.zjt.springboot.DeclareParents.Animal + represents all enhancement subclass of Animal 
     * 
     * = DuckFood.class defaultImpl represents a new class default to add 
     * / 
    the @DeclareParents (value = " . com.zjt.springboot.DeclareParents.Animal + ", defaultImpl = DuckFood class )
     public  static Food Food; 
}

　　Then there is the exciting part of the test:

public class Test {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext(AppConfiguration.class);
        Animal animal = (Animal)context.getBean("animal");
        animal.swim();
        Food food = (Food)animal;
        food.eat();

    }
}

Test Results:

Ducks like swimming. . . 
Ducks look good to eat. . .

Conclusion: From the test results, we found that only an animal Ducks acquired from the container, but you can get the ingredients feature set, and enhancements!