aspect oriented programming - fenix.tecnico.ulisboa.pt · summary problem aop.. aspect oriented...

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Summary Problem AOP

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...... Aspect Oriented Programming

Antonio Menezes Leitao

April 22, 2013

Antonio Menezes Leitao Aspect Oriented Programming

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Summary Problem AOP

...1 Problem

...2 AOPExampleJoin PointPointcutAdviceAspect


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Summary Problem AOP

.. Modularization.Concerns..

......

A software systems satisfies a set of concerns (requirements, usecases, features, data structures, patterns, colaborations,contracts, etc).In a functional decomposition, each concern is encapsulated inone or more functions.In an object-oriented decomposition, each concern is encapsulatedin one or more objects (or classes).It is difficult to simultaneously deal with all the concerns: only themost important ones are considered and they guide the principaldecomposition.The remaining concerns are implemented on top of the principaldecomposition, trying not to disturb it.


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Summary Problem AOP

.. Modularization.Cross-cutting Concern..

......

Some concerns crosscut the entire system (affecting all objects, classesor functions):

loggingsecuritysynchronizationmonitoring

.Cross-cutting Concern Implementation..

......

It is hard to find a decomposition that allows modularization ofconcerns that crosscut the entire system.The implementation of a cross-cutting concern becomes spread allover the system.


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Summary Problem AOP

.. Example: Apache Tomcat

.XML..

......


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Summary Problem AOP


.URL..

......


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Summary Problem AOP


.Logging..

......


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Summary Problem AOP

.. Modularization.Problems caused by Cross-cutting Concerns..

......

Code Tangling: Each module implements one fundamentalconcern and parts of other cross-cutting concerns.Code Scattering: Each cross-cutting concern is implemented byseveral fragments placed in different parts of the system.

.Consequences..

......

Low quality: code tangling facilitates errors.Low traceability: where is the code that implements a givenconcern? Which concern is implemented by this code?Low reusability: each module includes fragments that are notrelated to its task.Low evolvability: of modules that are fragmented and of modulesthat include fragments of other modules.


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Summary Problem AOP Example Join Point Pointcut Advice Aspect

.. Aspect-Oriented Programming

.History..

......

Invented at Xerox PARC (1995).Author: Gregor Kiczales (yes, he is the same author of the CLOSMOP).

.Fundamental Idea..

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Separation of Concerns for the concerns that affect the entiresystem.Concern implementation becomes centralized.Concern implementation includes a description of the places ofthe system that are affected by the concern.


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.. Concepts

.Dynamic Cross-Cutting..

......

Modification of the dynamic behavior of the program.Additional behavior that must be executed in well-defined pointsof the program execution.

.Static Cross-Cutting..

......

Modification of the static structure of the program.Modification of the class hierarchy, addition of methods,implementation of new interfaces, etc.


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.. Concepts

.Join Point..

......A join point is a well-defined point in the execution flow of a program.

.Pointcut..

......A pointcut is a set of join points and values in those points.

.Advice..

......An advice is a fragment of code that is executed at a given join point.


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.. Concepts

.Inter-Type Declaration..

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An inter-type declaration is a declaration that changes the staticstructure of a program (members of classes and relationships betweenclasses).

.Aspect..

......An (aspect) is a module that groups pointcuts, advices and inter-typedeclarations.


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.. Three Steps

.Decomposition..

......Requirements are decomposed in order to separate modular concernsfrom cross-cutting concerns.

.Implementation..

......Each concern is separately implemented, using OOP (for modularconcerns) or AOP (for cross-cutting concerns).

.Recomposition..

......The aspect weaving tool integrates the cross-cutting concerns with themodular concerns.


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.. Example

.Coordinates..

......

class XY {int x;int y;

XY(int x, int y) {this.x = x;this.y = y;

}

int getX() {return x;

}

int getY() {return y;

}}


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.. Example

.Shapes..

......class Shape {}


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.. Example

.Lines..

......

class Line extends Shape {XY origin;XY end;

XY getOrigin() {return origin;

}

XY getEnd() {return end;

}

void setOrigin(XY newOrigin) {origin = newOrigin;

}

void setEnd(XY newEnd) {end = newEnd;

}}


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.. Example

.Circles..

......

class Circle extends Shape {XY center;int radius;

XY getCenter() {return center;

}

int getRadius() {return radius;

}

void setCenter(XY newCenter) {center = newCenter;

}

void setRadius(int newRadius) {radius = newRadius;

}}


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.. Example

.Problem..

......Every time a shape is modified, we need to redraw.

.Solution..

......

...1 Identify all points where shapes are modified (pointcut).

...2 Execute a code fragment that causes redrawing, e.g.,Screen.redraw() (advice).


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.. Join Point

.Join Points..

......

method callconstructor callmethod executionconstructor executionadvice execution (advice over advice)field readingfield writingexception handlingstatic initialization (of classes)dinamic initialization (of instances)


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.. Pointcut.Pointcut..

......A pointcut selects points in the execution of a program that aredescribed by join points.

.Circle Changes..

......pointcut changeCircle():

call(void Circle.setCenter(XY)) ||call(void Circle.setRadius(int));

.Syntax..

......

Join points can be combined using operators:conjunction &&disjunction ||negation !


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.. Pointcut

.Syntax..

......

call(void Circle.setCenter(XY))Calls to the method named setCenter, defined in class Circle,with return type void and single parameter of type XY.call(void Circle.setCenter(XY)) ||call(void Circle.setRadius(int))Calls to the method named setCenter, defined in class Circle,with return type void and single parameter of type XY or to themethod named setRadius, defined in class Circle, with returntype void and single parameter of type int.


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.. Advice

.Advice..

......

An advice changes the program behavior in a pointcut.beforeafter returning, after throwing, afteraround

.Redraw the screen after each circle modification..

......after() returning: changeCircle() {

Screen.redraw();}

.What about instances of Line?..

......We need more flexible pointcuts.


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.. Pointcut

.Syntax..

......

call(void *.setCenter(XY))Calls to the method named setCenter, defined in any class, withreturn type void and single parameter of type XY.call(* *.set*(XY))Calls to any method whose name begins with set, defined in anyclass, with any return type and single parameter of type XY.call(* *.set*(..))Calls to any method whose name begins with set, defined in anyclass, with any return type and any number of parameters.


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.. Pointcut

.Crosscutting..

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name-based Explicit enumeration of method signatures (ex:call(void Circle.setCenter(XY))).

property-based Implicit enumeration based on method properties (ex:call(* *.set*(..))).

* Any number of characters except the dot... Any number of characters, including any

number of dots.+ Any subtype of the given type.

.Shape Setters........pointcut changeShape():

call(void Shape+.set*(..));


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.. Aspect

.Aspect..

......An aspect modularizes a cross-cutting concern, grouping pointcuts,advices and inter-type declarations.

.Shape Setters..

......

aspect ScreenUpdate {pointcut changeShape():

call(void Shape+.set*(..));

after() returning: changeShape() {Screen.redraw();

}}

.Problem..

......How to redraw just the modified shape?


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.. AspectJ

.Execution Context..

......

An advice can have parameters that become bound to parts of theexecution context that are exposed by the pointcut (using the joinpoints this, target and args).

.Shape Setters..

......

aspect ScreenUpdate {pointcut changeShape(Shape s):

call(void Shape+.set*(..)) && target(s);

after(Shape s) returning: changeShape(s) {Screen.redraw(s);

}}

.Problem..

......What about multiple screens?


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.. AspectJ.Inter-type Declarations........

Allow adding fields and methods to already defined classes.

.Shape Setters..

......

aspect ShapeListening {

private Vector<Screen> Shape.listeners = new Vector<Screen>();

public void Shape.addListener(Screen sc) {listeners.add(sc);

}

pointcut changeShape(Shape s):call(void Shape+.set*(..)) && target(s);

after(Shape sh): changeShape(sh) {for(Screen sc : sh.listeners) {

sc.redraw(sh);}

}

}


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.Shape Setters..

......

aspect ShapeListening {private Vector<Screen> Shape.listeners = new Vector<Screen>();


}



sc.redraw(sh);}

}

}


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.Shape Setters..

......



}


after(Shape sh): changeShape(sh) {

for(Screen sc : sh.listeners) {sc.redraw(sh);

}

}}


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.Shape Setters..

......



}



sc.redraw(sh);}

}}


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.. AspectJ

.Example..

......

Circle c = new Circle(new XY(10,20), 5);Line l = new Line(new XY(5,7), new XY(9,3));Screen sc0 = new Screen();Screen sc1 = new Screen();c.addListener(sc0);c.addListener(sc1);l.addListener(sc0);c.setCenter(new XY(1,2));l.setOrigin(new XY(3,4));

.Execution..

......

Redrawing Circle@123 screen Screen@321Redrawing Circle@123 screen Screen@654Redrawing Line@456 screen Screen@321

.Problem..

......What about multiple advices?


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.. AspectJ

.Example..

......

Circle c = new Circle(new XY(10,20), 5);Line l = new Line(new XY(5,7), new XY(9,3));

Screen sc0 = new Screen();Screen sc1 = new Screen();c.addListener(sc0);c.addListener(sc1);l.addListener(sc0);c.setCenter(new XY(1,2));l.setOrigin(new XY(3,4));

.Execution..

......


.Problem..



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.. AspectJ

.Example..

......

Circle c = new Circle(new XY(10,20), 5);Line l = new Line(new XY(5,7), new XY(9,3));Screen sc0 = new Screen();Screen sc1 = new Screen();

c.addListener(sc0);c.addListener(sc1);l.addListener(sc0);c.setCenter(new XY(1,2));l.setOrigin(new XY(3,4));

.Execution..

......


.Problem..



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.. AspectJ

.Example..

......

Circle c = new Circle(new XY(10,20), 5);Line l = new Line(new XY(5,7), new XY(9,3));Screen sc0 = new Screen();Screen sc1 = new Screen();c.addListener(sc0);c.addListener(sc1);l.addListener(sc0);

c.setCenter(new XY(1,2));l.setOrigin(new XY(3,4));

.Execution..

......


.Problem..



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.. AspectJ

.Example..

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.Execution..

......


.Problem..



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.. AspectJ

.Example..

......


.Execution..

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Redrawing Circle@123 screen Screen@321

Redrawing Circle@123 screen Screen@654Redrawing Line@456 screen Screen@321

.Problem..



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.. AspectJ

.Example..

......


.Execution..

......

Redrawing Circle@123 screen Screen@321Redrawing Circle@123 screen Screen@654

Redrawing Line@456 screen Screen@321

.Problem..



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.. AspectJ

.Example..

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.Execution..

......


.Problem..



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.. Aspect: Trace.Trace..

......

public aspect TraceChange {


before(Shape s): changeShape(s) {System.err.println("Changing " + s);

}

}

.Execution..

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Changing Circle@123Redrawing Circle@123 screen Screen@321Redrawing Circle@123 screen Screen@654Changing Line@456Redrawing Line@456 screen Screen@321

.Problem..

......Which call caused the trace?


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public aspect TraceChange {pointcut changeShape(Shape s):



}

}

.Execution..

......


.Problem..



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}}

.Execution..

......


.Problem..



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......




}}

.Execution..

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Changing Circle@123Redrawing Circle@123 screen Screen@321Redrawing Circle@123 screen Screen@654

Changing Line@456Redrawing Line@456 screen Screen@321

.Problem..



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......




}}

.Execution..

......


.Problem..



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}}

.Execution..

......


.Problem..

......Which call caused the trace?Antonio Menezes Leitao Aspect Oriented Programming

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......



before(Shape s): changeShape(s) {System.err.println("Changing " + s .+ " in " + thisJoinPoint);

}}

.Execution..

......

Changing Circle@123 in call(void Circle.setCenter(XY))Redrawing Circle@123 screen Screen@321Redrawing Circle@123 screen Screen@654Changing Line@456 in call(void Line.setOrigin(XY))Redrawing Line@456 screen Screen@321

.thisJoinPoint..

......Is bound to an object that describes the join point.Antonio Menezes Leitao Aspect Oriented Programming

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.. Aspect: Profiling

.New Operations for Circle..

......

class Circle extends Shape {...

void translate(XY offset) {setCenter(new XY(center.getX() + offset.getX(),

center.getY() + offset.getY()));}

void scale(int f) {setRadius(f * radius);translate(new XY(center.getX() * f,

center.getY() * f));}

}

.Challenge..

......How many shape changes are needed to implement a change of scale?


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.Aspect ScaleProfile..

......

aspect ScaleProfile {static int changeCount = 0;

pointcut changesMadeFromScale():call(void Shape+.set*(..)) && cflow(call(void *.scale(int)));

after(): changesMadeFromScale() {changeCount++;

}}

.cflow(call(void *.scale(int)))..

......Any join point in the control flow of the join pointcall(void *.scale(int)).


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.Example..

......

Circle c = new Circle(new XY(10,20), 5);System.err.println("(1) Shape changes: " + ScaleProfile.changeCount);c.setCenter(new XY(1,2));c.setRadius(1);System.err.println("(2) Shape changes: " + ScaleProfile.changeCount);c.scale(2);System.err.println("(3) Shape changes: " + ScaleProfile.changeCount);

.Execution..

......

(1) Shape changes: 0Changing Circle@123 in call(void Circle.setCenter(XY))Changing Circle@123 in call(void Circle.setRadius(int))(2) Shape changes: 0Changing Circle@123 in call(void Circle.setRadius(int))Changing Circle@123 in call(void Circle.setCenter(XY))(3) Shape changes: 2


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.. Aspect: Context Passing.Example..

......

public class Page {

Header header;Menu leftMenu;Content content;Footer footer;

Page() {header = new Header();leftMenu = new Menu();content = new Content();footer = new Footer();createBorder();

}

void createBorder() {new Line(new XY(0,0), new XY(10,0));new Line(new XY(10,0), new XY(10,10));new Line(new XY(10,10), new XY(0,10));new Line(new XY(0,10), new XY(0,0));

}}


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.. Aspect: Context Passing

.Example..

......

class Header {

Header() {createLeftHeader();createHeaderSeparator(2);createMiddleHeader();createHeaderSeparator(8);createRightHeader();

}

void createHeaderSeparator(int x) {new Line(new XY(x,8), new XY(x,10));

}

void createLeftHeader() { }

void createMiddleHeader() { }

void createRightHeader() { }}


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.. Aspect: Context Passing.Example..

......

public class ColoredPage extends Page {String color;

ColoredPage(String color) {super();this.color = color;

}

public static void main(String[] args) {ColoredPage cp = new ColoredPage("blue");

}}

.Problem..

......

How can we use the color of the ColoredPage as the color ofeach created Shape?It is not practical to pass the color as argument to each and everymethod that might create Shapes.


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.Aspect..

......

public aspect ColorizingAspect {

String Shape.color;

pointcut ShapeConstruction():call(Shape+.new(..));

pointcut ColoredPageConstructionCFlow(String color):cflow(call(ColoredPage.new(String))&& args(color));

after (String color) returning (Shape s):ShapeConstruction() &&ColoredPageConstructionCFlow(color) {

System.err.println("Changing color for " + s);s.color = color;

}}


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.Execution..

......

Changing color for Line@2e7263Changing color for Line@a59698Changing color for Line@16a55faChanging color for Line@32c41aChanging color for Line@e89b94Changing color for Line@13e205f

.Problem..

......What about changes after Shape construction?


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.Example..

......



}

void fillContent() {.new Circle(new XY(1,1), 4);

}

public static void main(String[] args) {ColoredPage cp = new ColoredPage("blue");System.err.println("About to fill content");cp.fillContent();

}}


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.Example..

......



}

void fillContent() {new Circle(new XY(1,1), 4);

}

public static void main(String[] args) {ColoredPage cp = new ColoredPage("blue");.System.err.println("About to fill content");.cp.fillContent();

}}


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.Execution..

......

Changing color for Line@2e7263Changing color for Line@a59698Changing color for Line@16a55faChanging color for Line@32c41aChanging color for Line@e89b94Changing color for Line@13e205fAbout to fill content

.Problem..

......The created Circle didn’t get the correct color?

.Solution..

......Another pointcut and another advice.


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.Aspect..

......


String Shape.color;

pointcut ShapeConstruction(): ...

pointcut ColoredPageConstructionCFlow(String color): ...

after (String color) returning (Shape s): ...

pointcut ColoredPageCFlow(ColoredPage cp):cflow(call(* *(..)) && target(cp));

after (ColoredPage cp) returning (Shape s):ShapeConstruction() &&ColoredPageCFlow(cp) {

System.err.println("Changing color for " + s);s.color = cp.color;

}}


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.Example..

......

Changing color for Line@2e7263Changing color for Line@a59698Changing color for Line@16a55faChanging color for Line@16a55faChanging color for Line@32c41aChanging color for Line@32c41aChanging color for Line@e89b94Changing color for Line@e89b94Changing color for Line@13e205fChanging color for Line@13e205fAbout to fill contentChanging color for Circle@5740bb

.Problem..

......The last four cases of Line are duplicated!


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.Aspect..

......


String Shape.color;





after (ColoredPage cp) returning (Shape s):ShapeConstruction() &&ColoredPageCFlow(cp) {


}}


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.Aspect..

......


String Shape.color;





after (ColoredPage cp) returning (Shape s):ShapeConstruction() &&ColoredPageCFlow(cp) &&! cflow(call(ColoredPage.new(String))) {


}}


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.Example..

......

Changing color for Line@2e7263Changing color for Line@a59698Changing color for Line@16a55faChanging color for Line@16a55faChanging color for Line@32c41aChanging color for Line@32c41aChanging color for Line@e89b94Changing color for Line@e89b94Changing color for Line@13e205fChanging color for Line@13e205fAbout to fill contentChanging color for Circle@5740bb


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.Example..

......

Changing color for Line@2e7263Changing color for Line@a59698Changing color for Line@16a55faChanging color for Line@32c41aChanging color for Line@e89b94Changing color for Line@13e205fAbout to fill contentChanging color for Circle@5740bb


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.. Pointcuts

.Objects..

......Represent all execution points where an object is an executor or areceptor or an argument or an exception.

.Example..

......

this(Foo)All execution points where this is an instance of class Foo.target(Foo)All execution points where the receptor of a method call is aninstance of class Foo.args(String,..,int)All execution points where the first argument is a String and thelast argument is an int.


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.. Pointcuts.Context Capture........Identical to the previous ones but these pointcuts can capture context..Example..

......

this(x)All execution points where this is an instance of the type ofparameter x, binding that parameter to that instance.target(x)All execution points where the receptor of a method call is aninstance of the type of the parameter x, binding that parameterto the receptor.args(String,..,x)All execution points where the first argument is a String and thelast argument is of the type of the parameter x, binding thatparameter to the argument.


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.. Pointcuts

.Method or Constructor Call..

......Represents the execution point after the argument evaluation butbefore execution of the called method or constructor..Example..

......

call(public void Foo.bar(Baz))All calls to a public method bar defined in class Foo that has aparameter of type Baz and that returns void.call(Foo+.new(..))All calls to constructors of class Foo or of any of its subclasses.


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.. Pointcuts

.Method or Construtor Execution..

......Represents the execution of a method or of a constructor.

.Example..

......

execution(public void Foo.bar(Baz))All executions of the public method bar defined in class Foo thathas a parameter of type Baz and that returns void.execution(Foo+.new(..))All executions of constructors of class Foo or of any of itssubclasses.


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.. Pointcuts

.Field Access..

......Represents field reading or writing.The assigned value can be captured with the pointcut args.

.Example..

......

set(int Foo.bar)All writings to field bar of an instance of Foo.get(PrintStream System.out)All readings from field out of class System.


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.. Pointcuts

.Field Access..

......

aspect LimitedBarFieldChange {

static final int MAX_BAR_CHANGE = 100;

before(Foo foo, int newBar):set(int Foo.bar) &&target(foo) &&args(newBar) {

if (Math.abs(newBar - foo.bar) > MAX_BAR_CHANGE) {throw new RuntimeException();

}}

}


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.. Pointcuts

.Exception Handling..

......

Represents the execution of an exception handler for a given type ofexception.The exception can be captured with the pointcut args.

.Example..

......

handler(IOException+)All executions of catch block that handles an IOException orany of its subclasses.handler(Foo*)All executions of catch block that handles exceptions of anyclasses whose name begins with Foo.


. . . . . .


.. Pointcuts

.Exception Handling..

......

aspect DumpFooException {

before(FooException e):handler(FooException) && args(e) {

e.printStackTrace();}

}


. . . . . .


.. Pointcuts.Class and Instance Initialization........Represents the execution of static initializers or instance initializers..Example..

......

staticinitialization(Foo)Execution of the static block of class Foo.preinitialization(Foo.new(..)))All executions of an instance initialization, from the beginning ofthe execution of the class constructor until the beginning of theexecution of the superclass constructor.initialization(Foo.new(..))All executions of an instance initialization, from the return of theexecution of the superclass constructor until the return of theexecution of the class constructor.


. . . . . .


.. Pointcuts

.Lexical Structure..

......

Represents all execution points within the lexical structure of a class(within(TypePattern)) or method(withincode(MethodOrConstructorSignature)), including internalclasses (annonymous or not).

.Example..

......

within(Foo)All execution points in the lexical scope of class Foo.withincode(* Foo.bar(..))All execution points in the lexical scope of any method namedbar of class Foo.


. . . . . .


.. Pointcuts

.Control Flow..

......Represents all execution points in the control flow of a given executionpoint.

.Example..

......

cflow(call(* Foo.bar(..)))All execution points in the control flow of a call to any methodnamed bar of class Foo, including the method call itself.cflowbelow(call(* Foo.bar(..)))All execution points in the control flow of a call to any methodnamed bar of class Foo, excluding the method call itself.


. . . . . .


.. Undoable Programs

.Problem..

......

We want to be able to undo the execution of Java programs.We want to be able to create checkpoints representing theexecution state of a Java program.We want to be able to force a program to go back in time until itreaches a given checkpoint.


. . . . . .



.A person has a name, an age, and a friend - Java..

......

class Person {String name;int age;Person friend;

public String toString() {return "[" + name + "," + age +

((friend == null) ? "" : " with friend " + friend) +"]";

}}

.Yes, I know:..

......

Missing constructor.Missing getters and setters.They are not relevant for the example.


. . . . . .


.Paul, John and Mary..

......

Person p0 = new Person() {{ name = "John"; age = 21; }};Person p1 = new Person() {{ name = "Paul"; age = 23; }};//Paul has friend named Johnp1.friend = p0;println(p1);//[Paul,23 with friend [John,21]]

int state0 = History.currentState();//32 years later, John changed is name to 'Louis'//and got a friendp0.age = 53;p1.age = 55;p0.name = "Louis";p0.friend = new Person() {{ name = "Mary"; age = 19; }};println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]int state1 = History.currentState();//15 years later, John (hum, I mean 'Louis') diedp1.age = 70;p1.friend = null;println(p1);//[Paul,70]//Let's go back in timeHistory.restoreState(state1);println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]//and againHistory.restoreState(state0);println(p1);//[Paul,23 with friend [John,21]]


. . . . . .



......

Person p0 = new Person() {{ name = "John"; age = 21; }};Person p1 = new Person() {{ name = "Paul"; age = 23; }};//Paul has friend named Johnp1.friend = p0;println(p1);//[Paul,23 with friend [John,21]]int state0 = History.currentState();//32 years later, John changed is name to 'Louis'//and got a friendp0.age = 53;p1.age = 55;p0.name = "Louis";p0.friend = new Person() {{ name = "Mary"; age = 19; }};println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]

int state1 = History.currentState();//15 years later, John (hum, I mean 'Louis') diedp1.age = 70;p1.friend = null;println(p1);//[Paul,70]//Let's go back in timeHistory.restoreState(state1);println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]//and againHistory.restoreState(state0);println(p1);//[Paul,23 with friend [John,21]]


. . . . . .



......

Person p0 = new Person() {{ name = "John"; age = 21; }};Person p1 = new Person() {{ name = "Paul"; age = 23; }};//Paul has friend named Johnp1.friend = p0;println(p1);//[Paul,23 with friend [John,21]]int state0 = History.currentState();//32 years later, John changed is name to 'Louis'//and got a friendp0.age = 53;p1.age = 55;p0.name = "Louis";p0.friend = new Person() {{ name = "Mary"; age = 19; }};println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]int state1 = History.currentState();//15 years later, John (hum, I mean 'Louis') diedp1.age = 70;p1.friend = null;println(p1);//[Paul,70]

//Let's go back in timeHistory.restoreState(state1);println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]//and againHistory.restoreState(state0);println(p1);//[Paul,23 with friend [John,21]]


. . . . . .



......

Person p0 = new Person() {{ name = "John"; age = 21; }};Person p1 = new Person() {{ name = "Paul"; age = 23; }};//Paul has friend named Johnp1.friend = p0;println(p1);//[Paul,23 with friend [John,21]]int state0 = History.currentState();//32 years later, John changed is name to 'Louis'//and got a friendp0.age = 53;p1.age = 55;p0.name = "Louis";p0.friend = new Person() {{ name = "Mary"; age = 19; }};println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]int state1 = History.currentState();//15 years later, John (hum, I mean 'Louis') diedp1.age = 70;p1.friend = null;println(p1);//[Paul,70]//Let's go back in timeHistory.restoreState(state1);println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]

//and againHistory.restoreState(state0);println(p1);//[Paul,23 with friend [John,21]]


. . . . . .



......

Person p0 = new Person() {{ name = "John"; age = 21; }};Person p1 = new Person() {{ name = "Paul"; age = 23; }};//Paul has friend named Johnp1.friend = p0;println(p1);//[Paul,23 with friend [John,21]]int state0 = History.currentState();//32 years later, John changed is name to 'Louis'//and got a friendp0.age = 53;p1.age = 55;p0.name = "Louis";p0.friend = new Person() {{ name = "Mary"; age = 19; }};println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]int state1 = History.currentState();//15 years later, John (hum, I mean 'Louis') diedp1.age = 70;p1.friend = null;println(p1);//[Paul,70]//Let's go back in timeHistory.restoreState(state1);println(p1);//[Paul,55 with friend [Louis,53 with friend [Mary,19]]]//and againHistory.restoreState(state0);println(p1);//[Paul,23 with friend [John,21]]


. . . . . .



.Save Program State..

......

import java.util.Stack;import java.lang.reflect.*;

public class History {

static Stack<ObjectFieldValue> undoTrail =new Stack<ObjectFieldValue>();

public static void storePrevious(Object object,String className,String fieldName,Object value) {

undoTrail.push(new ObjectFieldValue(object,className,fieldName,value));

}

. . .}


. . . . . .




......

import java.util.Stack;import java.lang.reflect.*;

public class History {

. . .

public static int currentState() {return undoTrail.size();

}

public static void restoreState(int state) {//undo all actions until size == statewhile (undoTrail.size() != state) {

undoTrail.pop().restore();}

}}


. . . . . .




......

class ObjectFieldValue {Object object;String className;String fieldName;Object value;

ObjectFieldValue(Object object,String className,String fieldName,Object value) {

this.object = object;this.className = className;this.fieldName = fieldName;this.value = value;

}

. . .}


. . . . . .




......

class ObjectFieldValue {

. . .

void restore() {try {

Field field =Class.forName(className).getDeclaredField(fieldName);

field.setAccessible(true);field.set(object, value);

} catch (ClassNotFoundException e) {throw new RuntimeException(e);

} catch (NoSuchFieldException e) {throw new RuntimeException(e);

} catch (IllegalAccessException e) {throw new RuntimeException(e);

}}

}


. . . . . .



.Javassist..

......

import javassist.*;import javassist.expr.*;import java.io.*;import java.lang.reflect.*;

public class Undoable {

public static void main(String[] args) throws . . . {if (args.length < 1) {

. . .} else {

Translator translator = new UndoableTranslator();ClassPool pool = ClassPool.getDefault();Loader classLoader = new Loader();classLoader.addTranslator(pool, translator);String[] restArgs = new String[args.length - 1];System.arraycopy(args, 1, restArgs, 0, restArgs.length);classLoader.run(args[0], restArgs);

}}

}


. . . . . .



.Javassist..

......

class UndoableTranslator implements Translator {

public void start(ClassPool pool)throws NotFoundException, CannotCompileException {

}

public void onLoad(ClassPool pool, String className)throws NotFoundException, CannotCompileException {CtClass ctClass = pool.get(className);makeUndoable(ctClass);

}

void makeUndoable(CtClass ctClass) {. . .

}}


. . . . . .



.Javassist..

......

void makeUndoable(CtClass ctClass)throws NotFoundException, CannotCompileException {final String template =

"{" +" History.storePrevious($0, \"%s\",\"%s\", ($w)$0.%s);" +" $0.%s = $1;" +"}";

for (CtMethod ctMethod : ctClass.getDeclaredMethods()) {ctMethod.instrument(new ExprEditor() {

public void edit(FieldAccess fa)throws CannotCompileException {if (fa.isWriter()) {

String name = fa.getFieldName();fa.replace(String.format(template,

fa.getClassName(),name, name, name));

}}

});}

}


. . . . . .



.AspectJ..

......

public aspect Undoable {

pointcut fieldWrite():set(* *.*) && within(UndoTest);

before(): fieldWrite() {Object obj = thisJoinPoint.getTarget();FieldSignature sig =

(FieldSignature)thisJoinPoint.getSignature();Field field = sig.getField();Class cls = field.getDeclaringClass();try {

History.storePrevious(obj, cls.getName(),field.getName(), field.get(obj));

} catch (IllegalAccessException e) {throw new RuntimeException(e);

}}

}


. . . . . .


.. Example

.Profiling..

......Measure the time taken to process requests.

.advice around..

......

public aspect ServletPerformanceMonitor {

Object around(HttpRequest request) :execution(* HttpServlet.do*(..)) && args(request,..) {

long startTime = System.nanoTime();Object retValue = proceed(request);long endTime = System.nanoTime();monitorAgent.record(request.getRequestURI(),

endTime - startTime);return retValue;

}

}


. . . . . .


.. Example

.Profiling..


.advice around..

......

public aspect ServletPerformanceMonitor {Object around(HttpRequest request) :

execution(* HttpServlet.do*(..)) && args(request,..) {long startTime = System.nanoTime();Object retValue = proceed(request);long endTime = System.nanoTime();monitorAgent.record(request.getRequestURI(),


}}


. . . . . .


.. Example

.Profiling..


.advice around..

......


execution(* HttpServlet.do*(..)) && args(request,..) {

long startTime = System.nanoTime();Object retValue = proceed(request);long endTime = System.nanoTime();monitorAgent.record(request.getRequestURI(),


}}


. . . . . .


.. Example

.Profiling..


.advice around..

......


execution(* HttpServlet.do*(..)) && args(request,..) {long startTime = System.nanoTime();

Object retValue = proceed(request);long endTime = System.nanoTime();monitorAgent.record(request.getRequestURI(),


}}


. . . . . .


.. Example

.Profiling..


.advice around..

......


execution(* HttpServlet.do*(..)) && args(request,..) {long startTime = System.nanoTime();Object retValue = proceed(request);

long endTime = System.nanoTime();monitorAgent.record(request.getRequestURI(),


}}


. . . . . .


.. Example

.Profiling..


.advice around..

......


execution(* HttpServlet.do*(..)) && args(request,..) {long startTime = System.nanoTime();Object retValue = proceed(request);long endTime = System.nanoTime();

monitorAgent.record(request.getRequestURI(),endTime - startTime);

return retValue;

}}


. . . . . .


.. Example

.Profiling..


.advice around..

......



endTime - startTime);

return retValue;

}}


. . . . . .


.. Example

.Profiling..


.advice around..

......




}}


. . . . . .


.. (Bad) Example

.Factorial (wrong)..

......

public class MyMath {

int fact (int n) {return -1;

}

public static void main(String[] args) {MyMath math = new MyMath();System.out.println(math.fact(10));

}}


. . . . . .


.. (Bad) Example

.Correcting Aspect..

......

aspect AroundFactorial {

int around (MyMath mm, int n):call(int fact(int)) &&target(mm) &&args(n) {

if (n == 0) {return 1;

} else {return n * mm.fact(n - 1);

}}

}


. . . . . .


.. Abstract Aspects

.AuthenticationAspect..

......

abstract aspect AuthenticationAspect {

abstract pointcut operationsNeeddingAuthentication();

before() : operationsNeeddingAuthentication() {

Authenticator.authenticate();}

}

.DatabaseAuthenticationAspect..

......

aspect DatabaseAuthenticationAspect extends AuthenticationAspect {

pointcut operationsNeeddingAuthentication():call(* DatabaseServer.connect());

}


. . . . . .


.. Attention

.Slot Access and Arithmetic Operation?..

......

class Foo {void main(String[] args) {

System.out.println(Foo.class);System.out.println(args[0] + args[1]);

}}

.Looks can be Deceiving..

......

Foo.class is implemented via Class.forName protected by anexception handler that catches ClassNotFoundException.The operador + applied to Strings is implemented via calls toStringBuffer.append.


. . . . . .


.AOP Problems..

......

Aspects might have excessive applicability. Java Annotationsmight provide a solution.Changes in the code might prevent the application of an aspect.IDEs (such as Eclipse) can detect those situations and inform theprogrammer.Programmers do not fully understand a program fragment unlessthey see all the injected advices. IDEs (such as Eclipse) allow easynavigation between injected advices.Some secury concerns: what if we inject return true in amethod that checks a password?


. . . . . .


G. Kiczales.Aspect-oriented programming.ACM Computing Surveys, 28(4es), December 1996.

G. Kiczales.AspectJ(tm): Aspect-oriented programming in Java.Lecture Notes in Computer Science, 2591:1, 2003.Gregor Kiczales.Aspect-oriented programming: A position paper from the XeroxPARC aspect-oriented programming project.In Max Muehlhauser, editor, Special Issues in Object-OrientedProgramming. Dpunkt Verlag, 1996.Gregor Kiczales and Erik Hilsdale.Aspect-oriented programming.In ESEC / SIGSOFT FSE, page 313, 2001.

Cristina Videira Lopes and Gregor Kiczales.Recent developments in AspectJ.


. . . . . .


In Cristina Lopes, Gregor Kiczales, Bedir Tekinerdogan,Wolfgang De Meuter, and Marco Meijers, editors, Workshop onAspect Oriented Programming (ECOOP 1998), June 1998.


aspect oriented programming - fenix.tecnico.ulisboa.pt · summary problem aop.. aspect oriented...

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