How to Implement Cross Cutting Concern using AOP in Scala

In this blog, I have explained that how easily we can implement Cross Cutting Concern such as logging using Aspect Oriented Programming in Scala. These concerns have nothing to do with core business logic. Aspect Oriented Programming is used for encapsulating cross-cutting concerns into re-usable modules. Here we used AspectJ weaver to weave precompiled aspects into project output

First we defined an annotation style aspect scala code:-

/**
* around execution of Sum
*/
@Around("execution(@com.<wbr />knoldus.aspect.Loggable * *.*(..))")
def aroundSum(joinPoint: ProceedingJoinPoint): Object = {
val result = joinPoint.proceed
println("Method:-" + joinPoint.toShortString() + " Input:-" + joinPoint.getArgs().toList.<wbr />mkString(",") + " Result:-" + result)
result
}

This aspect will print Method, its input and result detail, when a method is entered annotated with the @Loggable annotation and finished execution.

Let’s define the @Loggable annotation Java code

@Retention(RetentionPolicy.<wbr />RUNTIME)
@Target({ ElementType.METHOD })
public @interface Loggable {
}

Finally define a Sum class to see usage of Aspect

class Sum {
@Loggable
def checkSum(a: Int, b: Int): Int = a + b
}

We also need to add META-INF/aop.xml to configure aspect weaver.

<aspectj>

    <aspects>
        <!-- declare existing aspects to the weaver -->
        <aspect name="com.knoldus.aspect.AnnotationBasedAspect"/>

    </aspects>

    <weaver options="-verbose">
        <dump within="com.knoldus.*"/>
    </weaver>

</aspectj>

Complete source code can be found here CrossCuttingConcern_Scala.

Now run sbt test. You will see below message on console.

Method:-execution(Sum.checkSum(..)) Input:-2,3 Result:-5