Chapitre 6 Programmation orientée aspect (AOP)

Transcription

1 6 Programmation orientée aspect (AOP) 2I1AC3 : Génie logiciel et Patrons de conception Régis Clouard, ENSICAEN - GREYC «L'homme est le meilleur ordinateur que l'on puisse embarquer dans un engin spatial... et le seul qui puisse être produit en masse par du travail non qualifié.» Wernher von Braun

2 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 2

3 Cross-Cutting 3 Class A Class B Action1 Class C Action1 Action 2 Action 1 Action2 Action1 Example : Functional Integrity Constraint

4 Code-Scattering 4 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

5 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 5

6 Aspect Oriented Programming 6 OOP without aspect Class A Class B Class C OOP with aspect Class A Class B Class C Aspect

7 Definitions Aspect Joint Point Places where crosscutting concerns can be woven in. Ex. method call, field access, object creation. Pointcut Unit of modularity. Can contain fields and methods like a regular Java class. Declaration that selects join points and collects contexts at that point (regular expressions) Code Advice Code to be executed at a join point. 7

8 Illustration 8 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

9 Joint point models 9 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--;

10 Joint point models 10 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--;

11 Joint point models 11 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--;

12 Joint Point Models 12 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--;

13 Code Advice Code 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 After advice executes prior to the join point 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 13

14 Weaving An OAP application Set of classes Set of aspects Weaving Weaving rules specify how to integrate the final system 14

15 Types of Weaver 15 1/ Static weaver Source to source translation. Aspect code Class code Weaver Intermediate source code Compiler bytecode

16 Types of Weaver 16 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

17 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 17

18 Examples AspectJ (Open Source) Static weaver URL AspectJ Plug-in Eclipse 18

19 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"); 19

20 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"); 20

21 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); 21

22 Example 2: Debug (after weaving) 22 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);

23 Singleton OOP : Drawbacks Example 3: Design Pattern Revisited 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 23

24 Conclusion OOP + AOP = OOP AOP is available as extensions of many programming languages Java C++ Php C# D Smalltalk 24