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2I1AC3 : Génie logiciel et Patrons de conception
Chapitre 6
Programmation orientée aspect
« J'ai toujours rêvé d'un ordinateur qui soit aussi facile à utiliser qu'un téléphone. Mon rêve s'est réalisé.
Je ne sais plus comment utiliser mon téléphone »
Bjarne Stroustrup
Régis Clouard
regis.clouard@ensicaen.fr
ENSICAEN 14050 Caen
Introduction
 OOP




limitations
Code redundancy
Code tangling
 mix-up of multiple concerns at one place
Code scattering
 a concern is scattered over many places
Cross-cutting
 a concern than spans multiple units of OO modularity
 cannot be implemented without code-tangling and codescattering
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Cross-Cutting
Class A
Class B
Action1
Class C
Action1
Action 2
Action2
Action 1
Action1
 Example
: Functional Integrity Constraint
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Code-Scattering
Class A
Class B
Class C
call method 1
definition method 1
call method 2
call mthod 2
call method 1
call method 2
 Example:
Data Persistence
definition method 2
Solutions
 Respect
design principles of Chapter 1 !
 Aspect oriented Programming




Gregor Kiczales en 1996 à Xerox PARC
Inspiration: Artificial Intelligence
 Object language
 Meta-programming
 Reflection
New programming paradigm
Software programming history
 Procedural paradigm
 OOP paradigm
 OAP paradigm
– Separates business concerns from crosscutting concerns
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Aspect Oriented Programming
OOP without aspect
Class A
Class B Class C
OOP with aspect
Class A
Class B Class C
Aspect
Definitions
 Aspect


Unit of modularity.
Can contain fields and methods like a regular Java class.
 Joint


Point
Places where crosscutting concerns can be woven in.
Ex. method call, field access, object creation.
 Pointcut

Declaration that selects join points and collects contexts at that
point (regular expressions)
 Code

Advice
Code to be executed at a join point.
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Illustration
Object program
Class A
Class B
Joint Point
A1
Joint Point
B1
Joint Point
C1
Joint Point
A2
Joint Point
B2
Joint Point
C2
Joint Point
A3
Class C
Aspect program
Aspect
Pointcut1(A1,A2,B1,C2)
Pointcut2(A3,B2,C1,C2)
Pointcut1
Code advice 1
Pointcut1 & Pointcut2
Code advice 2
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Joint point models
Method call
public class HelloWorld {
private int max=10;
public static void main(String args[])
{
new HelloWorld().affichage();
}
public void affichage() {
for (int i=0;i<max;i++) {
try {
System.out.println("HelloWorld!");
} catch (Exception e) {
System.err.println("Problème d'affichage");
}
}
max--;
}
}
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Joint point models
Exception
public class HelloWorld {
private int max=10;
public static void main(String args[])
{
new HelloWorld().affichage();
}
public void affichage() {
for (int i=0;i<max;i++) {
try {
System.out.println("HelloWorld!");
} catch (Exception e) {
System.err.println("Problème d'affichage");
}
}
max--;
}
}
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Joint point models
Constructor call
public class HelloWorld {
private int max=10;
public static void main(String args[])
{
new HelloWorld().affichage();
}
public void affichage() {
for (int i=0;i<max;i++) {
try {
System.out.println("HelloWorld!");
} catch (Exception e) {
System.err.println("Problème d'affichage");
}
}
max--;
}
}
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Joint Point Models
Field access
public class HelloWorld {
private int max=10;
public static void main(String args[])
{
new HelloWorld().affichage();
}
public void affichage() {
for (int i=0;i<max;i++) {
try {
System.out.println("HelloWorld!");
} catch (Exception e) {
System.err.println("Problème d'affichage");
}
}
max--;
}
}
Code Advice
 Code
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advice is a method like construct that expresses the
action to be taken at the join points that are captured by a
pointcut.
 Before advice

executes prior to the join point
 After

advice
executes following the join point
 Around

advice
In such code advice, the keyword 'proceed' is used to specify
where to insert the join point’s execution
 can continue original execution, bypass execution or cause
execution with an altered context
 can cause execution of the join point multiple times
Weaving
 An


OAP application
Set of classes
Set of aspects
 Weaving

Weaving rules specify how to integrate the final system
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Types of Weaver
 1/

Static weaver
Source to source translation.
Aspect code
Class code
Weaver
Intermediate
source code
Compiler
bytecode
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Types of Weaver
 2/

Dynamic weaver
Bytecode enhancement, first compile source with original
compiler, then weave aspects into class files.
Weaver
Determine if a
code advice must
be executed
Class code
Pre-Weaver
modifies the
class code
Modifier
class code
Virtual
Machine
Bytecode
AOP Paradigm
 Separation


functional / non functional parts
Functional part: business concerns
 eg, Add or delete an employee
Non functional part: crosscutting concerns
 eg, Security and access control
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Examples
 AspectJ


(Open Source)
Static weaver
URL
 AspectJ
– http://www.eclipse.org/aspectj
 Plug-in Eclipse
– http://eclipse.org/ajdt
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Example 1: HelloWorld (before
weaving)
Hello.java
public class Hello {
public static void main(String a[]){
new Hello().sayHello();
}
}
World.aj
public aspect World {
pointcut salutation() : execution
(*Hello.sayHello(..));
public void sayHello() {
System.out.println("Hello!");
}
}
after() :salutation() {
System.out.println("Salut à toi
aussi");
}
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Example 1: HelloWorld (after
weaving)
Hello.java
public class Hello {
World.aj
public aspect World {
public static void main(String a[]) {
}
new Hello().sayHello();
System.out.println("Salut à toi
aussi");
public void sayHello() {
}
}
pointcut salutation() :execution
(*Hello.sayHello(..));
System.out.println("Hello!");
}
after() :salutation() {
System.out.println("Salut à toi
aussi");
}
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Example 2: Debug (before
weaving)
Debug.aj
Example2.java
public class Exemple2 {
private int _x=0;
public static void main(String args){
}
public aspect Debug {
pointcut methodEx2() :
execution(*Exemple2.*(..));
for (int i=0;i<10;i++) {
Exemple2.increment();
}
pointcut CallIncr() :
execution(*increment(..));
pointcut Ensemble() :
methodEx2() & CallIncr();
public void increment() {
}
_x++;
around() :Ensemble() {
}
System.out.println(x);
proceed
System.out.println(x);
}
}
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Example 2: Debug (after
weaving)
Example2.java
Debug.aj
Before weaving
After weaving
public class Exemple2 {
public aspect Debug {
private int _x=0;
pointcut methodEx2() :
execution(*Exemple2.*(..));
public static void main(String a[]){
for (int i=0;i<10;i++){
pointcut CallIncr() :
execution(*increment(..));
System.out.println(_x);
Exemple2.increment();
System.out.println(_x);
pointcut Ensemble() :
methodEx2() & CallIncr();
}
}
public void increment() {
}
_x++;
}
}
around() :Ensemble() {
System.out.println(_x);
proceed
System.out.println(_x);
}
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Example 3: Design Pattern
Revisited
 Singleton


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OOP : Drawbacks
Use of non classical constructor
Restrict inheritance
 Singleton AOP



Add a joint point cut on the constructor
An attribute stores the instance reference
The code advice returns a new instance (1st call) or the attribute
reference
Conclusion
 OOP
+ AOP = OOP
 AOP is available as extensions of many programming
languages






Java
C++
Php
C#
D
Smalltalk
 The
future of programming ?
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