在每个注解的构造函数之后自动设置属性

Question

i have a class. Something like this:

public class Example {
  public Example() {
    System.out.println("Constructor");
  }
}

Now i want to have an attribute "Version" which is given automatically after construction. Is it possible to resolve it per annotation? The best solution would be, if i could write a annotation like @VersionControl above some classes and then another module sets an attribute "version" for the classes.

Something like this:

@VersionControl
public class Example {

  int version; //this should be set automatically

  public Example() {
    System.out.println("Constructor");
  }
}

Is it possible? Thx for your help!

Answer 1

My solution with annotation and aspectj:

Annotation:

@Target(ElementType.TYPE)
   public @interface MyAnnotation{
}

Aspect:

@Aspect
public class MyAspect {

  @Pointcut("execution((@MyAnnotation *).new(..))")
   public void bla() {
   }

  @After("bla()")
   public void after(JoinPoint joinPoint) {
    try {
     joinPoint.getTarget().getClass().getDeclaredField("version").set(joinPoint.getTarget(), VersionProvider.getVersion());
    } catch (IllegalAccessException | NoSuchFieldException e) {
      e.printStackTrace();
    }
  }
}

Example object:

@MyAnnotation
public class Example {

 public long version;

 public long getDarwinVersion() {
    return version;
 }

}

In this solution, the version will be set after the constructor of the annotated class was called.