Aspect-Oriented Software Development (AOSD) Tutorial #3 AspectJ - continued

Aspect-Oriented Software Development (236608) 2 Today: AspectJ - Continued Additional pointcut types –cflow –cflowbelow Intertype declarations Compilation errors declarations Examples English – AspectJ phrase book (selected entries)

Aspect-Oriented Software Development (236608) 3 Task 1: Greeting before printing Public class Test { public static void main(String[] args) { f(); } static void f() { g(); } static void g() { System.out.println( “ message from g ” ); } Task: Before each printing operation, print a greeting message

Aspect-Oriented Software Development (236608) 4 English – AspectJ Phrase Book (3) pointcut exceptF(): withincode(void Test.f()); after() throwing : exceptF() { … } “All the exceptions thrown by f()” “All the exceptions thrown while f() is executed:” pointcut exceptF2(): cflow(call(void Test.f())); after() throwing : exceptF2() { … }

Aspect-Oriented Software Development (236608) 5 English – AspectJ Phrase Book (4) pointcut exceptTest(): within (Test); after() throwing : exceptTest() { … } “All the exceptions thrown by functions of class Test” What is the relationship between: (1) pointcut except1(): cflow(call(void Test.g())); (2) pointcut except2(): cflowbelow(call(void Test.f())); Equality!

Aspect-Oriented Software Development (236608) 6 Task 1: Proposed solution-1 public aspect Printing { pointcut fPC(): execution(void Test.f()); pointcut gPC(): execution(void Test.g()); pointcut printPC(): call(void java.io.PrintStream.println(String)); before(): cflow(fPC()) && cflow(gPC()) && printPC() { System.out.println("hello"); } before(): cflow(fPC() && gPC()) && printPC() { System.out.println("shalom"); } matched by printPC pointcut!

Aspect-Oriented Software Development (236608) 7 Task 1: Proposed solution-2 public aspect Printing { pointcut fPC(): execution(void Test.f()); pointcut gPC(): execution(void Test.g()); pointcut printPC(): call(void java.io.PrintStream.println(String)); before(): cflow(fPC()) && cflow(gPC()) && printPC() && !within(Printing) { System.out.println("hello"); } before(): cflow(fPC() && gPC()) && printPC() && !within(Printing) { System.out.println("shalom"); } can not be matched! (f() and g() have no common join-points) Output: hello message from g

Aspect-Oriented Software Development (236608) 8 Cflow Pointcuts Combination P Q cflow(P) cflow(Q)cflow(P) && cflow(Q) P && Q cflow(P && Q)

Aspect-Oriented Software Development (236608) 9 Example Class: Point - reminder class Point { private int x, y; public Point(int x, int y) { this.x = x; this.y = y; } public void setX(int x) { this.x = x; } public void setY(int y) { this.y = y; } public void MoveTo(Point p) {setX(p.x); setY(p.y); } public int getX() { return x; } public int getY() { return y; } }

Aspect-Oriented Software Development (236608) 10 Task 2: Named Points Task2: Every point should have a name, and each time the point is moved, the user should get a message with the name of the point and its new coordinates. Pontcut = ? pointcut moved(Point pt): target(pt) && (call(void setX(int)) || call(void setY(int)));

Aspect-Oriented Software Development (236608) 11 Task 2 – contd. Advice = ? Add the “name” field to Point // Inside the aspect body! private String Point.name = ""; public String Point.getName() {return name;} public void Point.setName(String newName) {name = newName;} Who can access the “name” field = ? Only the aspect! (private field of the aspect) Who can access getName(), setName()? Everybody! (public access) inter-type declarations

Aspect-Oriented Software Development (236608) 12 Task 2 – version2. Another way to add the “name” field to Point Assume there is a class NamedObject in a base system: public class NamedObject { private String name; … public NamedObject() {this.name = "";} … public void setName(String newName) {this.name = newName;} public String getName() {return this.name;} } declare parents: Point extends NamedObject; Add to the aspect:

Aspect-Oriented Software Development (236608) 13 Task 2 – contd. Advice = ? – contd. Advice type = ? after returning The advice: after(Point pt) returning: moved (pt) { System.out.println("Point "+pt.getName()+" moved to ("+pt.getX()+","+pt.getY()+")"); }

Aspect-Oriented Software Development (236608) 14 Task 2 – contd. Is that enough to add the name? Theoretically, yes. But we’d better have some initialization For example: When point number “i” is created, give it the name “Pointi” How? – Task 2-A –“around” constructor calls –generate the needed name –set the generated value to the name field

Aspect-Oriented Software Development (236608) 15 Task 2-A pointcut createPoint(int x, int y): args(x,y) && call(Point.new(..)); Pointcut = ? (reminder) Advice = ? Point around(int x, int y): createPoint(x,y){ Point newPoint = proceed(x,y); … //generate name newPoint.setName( … ); //update the “ name ” field return newPoint; }

Aspect-Oriented Software Development (236608) 16 Task 2-A – contd. private int pointsCounter = 0; Name generation: - add points counter to the aspect! Advice as a whole: Point around(int x, int y): createPoint(x,y){ Point newPoint = proceed(x,y); return newPoint; } pointsCounter ++; newPoint.setName("Point"+pointsCounter);

Aspect-Oriented Software Development (236608) 17 Task 3: Contract Enforcement Example aspect RegistrationProtection { pointcut register(): call(void Registry.register(FigureElement)); pointcut canRegister(): withincode(static *FigureElement.make*(..)); before(): register() && !canRegister() { throw new IllegalAccessException("Illegal call " + thisJoinPoint); } } Constraint : only the factory methods can add an element to the registry of figure elements. Meaning: ensures that no figure element is added to the registry more than once. Implementation: Not an elegant solution! Can be solved at compilation time, and not at runtime

Aspect-Oriented Software Development (236608) 18 More to Inter-type Declarations declare error: Pointcut: String; declare warning: Pointcut: String; New powerful types of compilation warnings and errors! Syntax: For the contract enforcement example: For example, to identify method calls that should not exist in a correct program aspect RegistrationProtection { pointcut register(): call(void Registry.register(FigureElement)); pointcut canRegister(): withincode(static *FigureElement.make*(..)); } declare error: register() && !canRegister(): "Illegal call" Attention! Only static information will be used at the join-points!

Aspect-Oriented Software Development (236608) 19 More to AspectJ: Subtypes at pointcuts Example base classes: public class NamedObject { …} public class NamedFigure extends NamedObject { …} Example aspect: public aspect NamedObjectsObserver { …}

Aspect-Oriented Software Development (236608) 20 Subtypes at pointcuts – contd. class public aspect NamedObjectsObserver { //matches calls to functions of NamedObject only pointcut publicCalled1(): call(public * NamedObject.*(..)); //matches calls to functions of NamedObject and of NamedFigure pointcut publicCalled2(): call(public * NamedObject+.*(..)); //matches calls to functions of NamedFigure only pointcut publicCalled3(): call(public * (NamedObject+ && !NamedObject).*(..)); after() : publicCalled1() { System.out.println("Public (1)"+thisJoinPoint); } after() : publicCalled2() { System.out.println("Public (2)"+thisJoinPoint); } after() : publicCalled3() { System.out.println("Public (3)"+thisJoinPoint); } }