CS 683 Emerging Technologies Spring Semester, 2003 AspectJ Syntax 3
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Non-Singleton Aspects

percflow
perthis

Privileged Aspects
Information about Join Points
Order & Conflicts Among Aspects

Doc 5, AspectJ Syntax 3 Slide # 2

Non-Singleton Aspects

An instance of the aspect is created for every object that is the executing object of any join points of the Pointcut

An instance of the aspect is created for every object that is the target object of any join points of the Pointcut

ajc would not compile examples with pertarget

An instance of the aspect is created for flow of control of the join points of the Pointcut

Created when flow in entered

An instance of the aspect is created for flow of control of the join points of the Pointcut

Created when flow in entered

Doc 5, AspectJ Syntax 3 Slide # 3

public class Hello {
    void b() {
      System.out.println("In b");
   }
} 

Doc 5, AspectJ Syntax 3 Slide # 4

percflow

public  aspect HelloAspect percflow(methodCall() ) {
   
   private int callCount = 0;
   private static int totalCount = 0;
   
   public int getCount() {
      return callCount;
   }
   
   public int getTotalCount() {
      return totalCount;
   }
   
   public static void main(String[] arguments ) {
      Hello example = new Hello();
      example.b();
      HelloAspect aspect = HelloAspect.aspectOf();
      System.out.println( "Object Count is " + aspect.getCount()
         + " Total count " + aspect.getTotalCount() );
   }
   
   pointcut methodCall() : call(* *(..) );
   
   before(): methodCall() {
      callCount++;
      totalCount++;
   }

Doc 5, AspectJ Syntax 3 Slide # 5

perthis

public  aspect HelloAspect perthis(methodCall() ) {
   private int callCount = 0;
   private static int totalCount = 0;
   public int getCount() {
      return callCount;
   }
   public int getTotalCount() {
      return totalCount;
   }
   public static void main(String[] arguments ) {
      Hello example = new Hello();
      example.b();
      example.b();
      (new Hello()).b();
      HelloAspect aspect = HelloAspect.aspectOf(example);
      System.out.println( "Object Count is " + aspect.getCount()
         + " Total count " + aspect.getTotalCount() );
   }
   pointcut methodCall() : call(* *(..) );
   before(): methodCall() {
      callCount++;
      totalCount++;
   }
} 

In b
In b
In b
Object Count is 2 Total count 3

Doc 5, AspectJ Syntax 3 Slide # 6

Privileged Aspects

public class Hello {
    private void b() {
      System.out.println("In b");
   }
} 

public privileged  aspect HelloAspect {
   public static void main(String[] arguments ) {
      Hello example = new Hello();
      example.b();
   }
} 

Doc 5, AspectJ Syntax 3 Slide # 7

/*   Generated by AspectJ version 1.0.6 */
   
public class Hello {
  private void b() {
    System.out.println("In b");
  } 
   
  public Hello() {
    super();
  }
    
  public final void b$ajc$backdoor() {
    this.b();
  } 
} 

Doc 5, AspectJ Syntax 3 Slide # 8

Information about Join Points

Provide information about the join point selected by a pointcut

public class Hello {
    int b(int foo, String bar) {
      System.out.println("In b");
      return foo + 1;
   }
} 

Doc 5, AspectJ Syntax 3 Slide # 9

import org.aspectj.lang.*;
import org.aspectj.lang.reflect.CodeSignature;
public privileged  aspect HelloAspect {
   public static void main(String[] arguments ) {
      Hello example = new Hello();
      int answer = example.b(5, "cat");
   }
   Object around() : call(* b(..) ) {
      System.out.println("Intercepted message: " +
         thisJoinPointStaticPart.getSignature().getName());
      System.out.println("In class: " +
         thisJoinPointStaticPart.getSignature().getDeclaringType().getName());
      printParameters(thisJoinPoint);
      Object result = proceed();
      System.out.println( "Result " + result);
      return result;
   }
   private void printParameters(JoinPoint jp) {
      System.out.println("Arguments: " );
      Object[] args = jp.getArgs();
      String[] names = ((CodeSignature)jp.getSignature()).getParameterNames();
      Class[] types = ((CodeSignature)jp.getSignature()).getParameterTypes();
      for (int i = 0; i < args.length; i++) {
         System.out.println(" " + i + ". " + names[i] +
            " : " + types[i].getName() +
            " = " + args[i]);
      }
   }
 }
Doc 5, AspectJ Syntax 3 Slide # 10

Doc 5, AspectJ Syntax 3 Slide # 11

Order & Conflicts Among Aspects

Doc 5, AspectJ Syntax 3 Slide # 12

• If aspect A dominates aspect B, then advice in A has precedence over advice in B.

   aspect B { blah
   }
   aspect A dominates B { blah
   }

• If aspect A is a subaspect of aspect B, then advice in A has precedence over advice in B.

   abstract aspect B {
   }
   public aspect A extends B {
   }

• Unless otherwise specified with the dominates keyword, advice in a subaspect dominates advice in a superaspect.

• Otherwise, if two pieces of advice are defined in two different aspects, it is undefined which one has precedence.

Doc 5, AspectJ Syntax 3 Slide # 13

• If either are after advice, then the one that appears later in the aspect has precedence over the one that appears earlier.

• Otherwise, then the one that appears earlier in the aspect has precedence over the one that appears later.

aspect A {
   before(): execution(void main(String[] args)) {}
   after(): execution(void main(String[] args)) {}
   before(): execution(void main(String[] args)) {}
}

Doc 5, AspectJ Syntax 3 Slide # 14

If calls proceed then advice with next precedence is run

Otherwise advice with lower precedence at this join point is not run

If throws an exception advice with lower precedence is not run

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