Custom Java annotation to skip the method execution

Question

I want to create a custom annotation to skip method execution

This is my annotation code, with the validator class

@Target({ METHOD , FIELD , PARAMETER } )
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy={MyValidator .class})
public @interface MyAnnotation {

    String message() default "DEFAULT_FALSE";

    Class<?>[] groups() default{};

    Class<? extends Payload>[] payload() default{};

}

I tried it with validator. This is how my validator looks like

public class MyValidator implements ConstraintValidator<MyAnnotation, String >{

    @Override
    public void initialize(MyAnnotation arg0) {

    }

    @Override
    public boolean isValid(String arg0, ConstraintValidatorContext arg1) {

        if(str=="msg"){
            return true;
        }
        return false;
    }

}

And this is how I want to use -- I want to use the annotation on method level and to skip the method execution.

I don't know if it is possible.. Please help.

public class Test {



    public static void main(String[] args) {
    Test t = new Test();
        boolean valid=false;

         valid=t.validate();
        System.out.println(valid);

    }

@MyAnnotation(message="msg")
    public boolean validate(){

     // some code to return true or false
    return true;


    }
}

Answer 1

You should use AOP for that. Create a AspectJ project, and try something like this:

MyAnnotation.java:

package moo.aspecttest;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(value = { ElementType.METHOD })
public @interface MyAnnotation
{
    public String value();
}

MyAspectClass.java:

package moo.aspecttest;

import java.lang.reflect.Method;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;

@Aspect
public class MyAspectClass
{

    @Around("execution(* *(..))")
    public Object aroundAdvice(ProceedingJoinPoint point) throws Throwable
    {
        Method method = MethodSignature.class.cast(point.getSignature()).getMethod();
        String name = method.getName();
        MyAnnotation puff = method.getAnnotation(MyAnnotation.class);
        if (puff != null) {
            System.out.println("Method " + name + " annotated with " + puff.value() + ": skipped");
            return null;
        } else {
            System.out.println("Method " + name + " non annotated: executing...");
            Object toret = point.proceed();
            System.out.println("Method " + name + " non annotated: executed");
            return toret;
        }
    }
}

MyTestClass.java:

package moo.aspecttest;

public class MyTestClass
{

    @MyAnnotation("doh")
    public boolean validate(String s) {
        System.out.println("Validating "+s);
        return true;
    }

    public boolean validate2(String s) {
        System.out.println("Validating2 "+s);
        return true;
    }

    public static void main(String[] args)
    {
        MyTestClass mc = new MyTestClass();

        mc.validate("hello");
        mc.validate2("cheers");

        }
    }
}

output generated when you run it:

Method main non annotated: executing...
Method validate annotated with doh: skipped
Method validate2 non annotated: executing...
Validating2 cheers
Method validate2 non annotated: executed
Method main non annotated: executed

I used a very generic aroundAdvice, but you can use a beforeAdvice, if you want. Indeed, I think that point is clear.

Answer 2

It is actually very simple, sort of the simplest aspect one can write. ;-)

The ugly thing about your sample code is that it uses several classes for which you do not show the source code, so I had to create dummy classes/interfaces in order to make your code compile. You also do not show how the validator is applied, so I have to speculate. Anyway, here is a fully self-consistent set of sample classes:

Helper classes:

This is just scaffolding in order to make everything compile.

package de.scrum_master.app;

public interface Payload {}

package de.scrum_master.app;

public class ConstraintValidatorContext {}

package de.scrum_master.app;

public @interface Constraint {
  Class<MyValidator>[] validatedBy();
}

package de.scrum_master.app;

import java.lang.annotation.Annotation;

public interface ConstraintValidator<T1 extends Annotation, T2> {
  void initialize(T1 annotation);
  boolean isValid(T2 value, ConstraintValidatorContext validatorContext);
}

package de.scrum_master.app;

public class MyValidator implements ConstraintValidator<MyAnnotation, String> {
  @Override
  public void initialize(MyAnnotation annotation) {}

  @Override
  public boolean isValid(String value, ConstraintValidatorContext validatorContext) {
    if ("msg".equals(value))
      return true;
    return false;
  }
}

package de.scrum_master.app;

import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.*;

import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.*;

@Target({ METHOD, FIELD, PARAMETER })
@Retention(RUNTIME)
@Constraint(validatedBy = { MyValidator.class })
public @interface MyAnnotation {
  String message() default "DEFAULT_FALSE";
  Class<?>[] groups() default {};
  Class<? extends Payload>[] payload() default {};
}

Driver application:

If you want to test something, you do not just need a positive test case, but also a negative one. Because you did not provide that, user Sampisa's answer was not what you were looking for. BTW, I think you should have been able to deduce from it the solution by yourself. You did not even try. Do you not have any programming experience?

package de.scrum_master.app;

public class Application {
  public static void main(String[] args) {
    Application application = new Application();
    System.out.println(application.validate1());
    System.out.println(application.validate2());
  }

  @MyAnnotation(message = "execute me")
  public boolean validate1() {
    return true;
  }

  @MyAnnotation(message = "msg")
  public boolean validate2() {
    return true;
  }
}

Aspect:

The only reason why I add another sample aspect in addition to Sampisa's is that his solution is suboptimal with regard to his reflection usage. It is ugly and it is slow. I think my solution is a bit more elegant. See for yourself:

package de.scrum_master.aspect;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class SkipValidationAspect {
  @Around("execution(@de.scrum_master.app.MyAnnotation(message=\"msg\") boolean *(..))")
  public boolean skipValidation(ProceedingJoinPoint thisJoinPoint) throws Throwable {
    return false;
  }
}

Very simple, is it not?

Console log:

true
false

Et voilà - I think this is what you were looking for.