Java - Defining and accessing annotations?

Question

I have an abstract class called Client. How can I get access to an annotation that was declared on the calling method on the child class? What's the best way to handle this?

public abstract class Client {

   protected void synchronize() {

      // How can I get the Annotation defined on inheriting class?   
      StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();
      StackTraceElement lastStackElement =       stackTraceElements[stackTraceElements.length-1] ;
      Method m = this.getClass().getMethod(lastStackElement.getMethodName(),       String.class, int.class);
      m.getAnnotation(Cache.class);

      // synchronize data from server
   }

}

.

public class OrderClient extends Client {

   @Cache(minute = 5)
   public void synchronizrWithCustomerId(String customerId) {

      // So some stuff setup body and header

      super.synchronize();
   }

}

probably something along the lines of what you just wrote down. just cache the results by classname+methodname to avoid repeated reflection — radai
– radai, Commented Dec 27, 2012 at 6:58

Andremoniy · Accepted Answer · 2019-08-29 08:34:07Z

2

Based on your example this code works well:

public class TestS1 {

    public abstract class Client {

        protected void synchronize() throws NoSuchMethodException {
            // How can I get the Annotation defined on inheriting class?
            StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();
            StackTraceElement lastStackElement = stackTraceElements[2];

// take attention here: stackTraceElements[2]

     Method m = this.getClass().getMethod(lastStackElement.getMethodName(), String.class);
            Cache annotation = m.getAnnotation(Cache.class);
            System.out.println("Cache.minute = " + annotation.minute());
            // synchronize data from server
        }
    }

also you need to mark your annotation with @Retention(RetentionPolicy.RUNTIME)

    @Retention(RetentionPolicy.RUNTIME)
    @interface Cache {
        int minute();
    }

    public class OrderClient extends Client {
        @Cache(minute = 5)
        public void synchronizrWithCustomerId(String customerId) throws NoSuchMethodException {
            // So some stuff setup body and header
            super.synchronize();
        }
    }

    public void doTest() throws NoSuchMethodException {
        OrderClient oc = new OrderClient();
        oc.synchronizrWithCustomerId("blabla");
    }

    public static void main(String[] args) throws NoSuchMethodException {
        TestS1 t = new TestS1();
        t.doTest();
    }

}

Output is: Cache.minute = 5

edited Aug 29, 2019 at 8:34

answered Dec 27, 2012 at 7:14

Andremoniy

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7 Comments

aryaxt Over a year ago

What does retention do? and is it possible to implement it in 1 place instead of every synchronize method? thanks

Andremoniy Over a year ago

@aryaxt Retention(RUNTIME) is needed to provide accessing to your annotaitons in Runtime (see also: stackoverflow.com/questions/2286998/…). I don't understand second part of your question about implementing it in 1 place. If it about Retention, so you need to annotate with it only Cache interface.

aryaxt Over a year ago

I got this error while annotating retention. The annotation @Retention is disallowed for this location.

Andremoniy Over a year ago

I didn't find @Json annotation (could you provide URL link?), but for example here they really use Retention(RUNTIME): github.com/FasterXML/jackson-annotations/blob/master/src/main/…

aryaxt Over a year ago

Sorry I was wrong, I realized that Retention should be on annotation class

|

aryaxt · Accepted Answer · 2012-12-27 07:35:40Z

0

Andremoniy answer is absolutely correct. The only thing I changed was the way i lookup in the stack-trace.

    Cache cache = null;

    try {
        StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();

        for (StackTraceElement element : stackTraceElements) {
            if (this.getClass().getName().equals(element.getClassName())) {
                Method method = this.getClass().getMethod(element.getMethodName(), String.class);
                cache = method.getAnnotation(Cache.class);
                break;
            }
        }
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    }

answered Dec 27, 2012 at 7:35

aryaxt

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