Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

1/24

Introduction toAspect-Oriented Software

Development

Bruno Harbulot

ESNW, the University of Manchesterhttp://www.cs.man.ac.uk/~harbulob/

ELF Developers' Forum – Manchester - October 2005

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

2/24

Presentation outline

● Problem: code-tangling● Concepts of Aspect-Oriented Programming● AOP Tools

– AspectJ

● Applications: Design pattern example● Conclusions

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

3/24

Problem presentation

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

4/24

good modularity

● URL pattern matching in org.apache.tomcat– red shows relevant lines of code– nicely fits in two boxes (using inheritance)

URL pattern matching

(c) Copyright 1998-2002 Palo Alto Research Center Incroporated. All rights reserved.

Sour

ce:

http

://w

ww

.ecl

ipse

.org

/asp

ectj

/tea

chin

g.ph

p

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

5/24

problems like…

● logging in org.apache.tomcat– red shows lines of code that handle logging – not in just one place– not even in a small number of places

logging is not modularized

(c) Copyright 1998-2002 Palo Alto Research Center Incroporated. All rights reserved.

Sour

ce:

http

://w

ww

.ecl

ipse

.org

/asp

ectj

/tea

chin

g.ph

p

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

6/24

Conceptsof

Aspect-OrientedProgramming

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

7/24

Crosscutting concerns

● Concern: “specific requirement or consideration that must be addressed in order to satisfy the overall system goal” [Lad03]

● Designing software: separating concerns into units such as procedures, classes, methods, libraries, etc.

● Two concerns crosscut each other when their relation implies tangled code.

● Crosscutting concern: concern that crosscuts the main purpose of a unit, or that is spanned across multiple units.

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

8/24

Motivation forAspect-Oriented Programming

● Programming paradigm for encapsulating crosscutting concerns.

● AOP builds on top of other programming paradigms: object-oriented, procedural or functional. It does not supplant them.

● Encapsulate crosscutting concerns into aspects.

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

9/24

Concepts of AOP (I)

● Aspect: unit encapsulating a crosscutting concern.● Join point: point in the execution of a program

where an aspect might intervene.● “[...] whenever condition C arises, perform action

A” [Fil05]

– Pointcut: expression of a subset of join points (condition C)

– Advice: piece of code for action A.– Pointcuts and advice encapsulated into aspects.

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

10/24

Concepts of AOP (II)

● AOP is not about “patching” pieces of code.

● AOP is about performing an action systematically upon recognition of a behaviour in the code.

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

11/24

Concepts of AOP (III)

● Weaving

Base units

Aspects

Weaver Application

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

12/24

Aspect-OrientedProgramming

Tools

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

13/24

AOP Tools

● (Java-based tools)● Languages:

– AspectJ (now merged with AspectWerkz)

● Frameworks (mainly for J2EE applications):– JAC– Jboss AOP

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

14/24

AspectJ

● Aspect-Oriented extension to Java.● Aspect language (new constructs for aspects).

● Produces standard Java bytecode.● Weaves into class files.

.class.java

.aj

Weaver .class

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

15/24

AspectJ example: pre-condition

/* Java code */class Test { public int val ;

/* ... */}

/* AspectJ code */aspect Precondition { public static final int MAX_VALUE = 2000 ; before(int newval): set (int Test.val) && args (newval) { if (newval > MAX_VALUE) throw new RuntimeException(“Invalid value”); }}

Piece of advice Pointcut

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

16/24

AspectJ example: persistence

aspect DatabaseAspect { pointcut transactionalMethods (): execution (/* pattern for transactional methods */) ;

before(): transactionalMethods () { initialiseDatabase() ; }

after() returning: transactionalMethods() { commitTransaction() ; }

after() throwing: transactionalMethods() { rollbackTransaction() ; }}

(Soares et. al. Implementing distribution and persistence aspects with AspectJ.)

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

17/24

AspectJ – Pointcuts

● Pointcuts define where to intervene● Expressed from primitive pointcuts:

– call/execution(<Method signature>)– set/get(<Field signature>)– cflow(<Pointcut>)– args, target, this

● pointcut setvalue(int val):call(public void set*(int)) && args(val);

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

18/24

Application:Design patterns

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

19/24

Observer pattern (I)

● In Java, explicit “addObserver” and “notify” embedded the observed class.

● “Observable” feature tangled with the main purpose of the class.

● public void process() { /* Do something */ notifyObservers();}

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

20/24

Observer pattern (II)

● In AspectJ, possible to decouple the “observable” from the main purpose of the class.

● after(): execution(* *.process(..)) { /* notify or perform an action */}

● The “observer” and “observable” can be encapsulated into a single aspect.

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

21/24

Conclusions

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

22/24

Benefits and pitfalls

● Benefits: clearer decomposition of the roles (more reusability)

● Pitfalls:– Learning curve to comprehend the concepts

(eased by Java environment)– Need for tools to understand the overall

behaviour of the application (Eclipse AJDT)http://www.eclipse.org/ajdt/(available for other IDEs as well)

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

23/24

References (I)

● AOSD website: http://www.aosd.net/

● AspectJ: http://www.eclipse.org/aspectj/

● “Foundations of AOP for J2EE Development”by R. Pawlak et al., ISBN: 1590595076

● “Eclipse AspectJ” by A. Colyer et al.,ISBN: 0321245873

● [Lad03] “AspectJ in Action” by R. Laddad,ISBN: 1930110936

● [Fil05] “Aspect-Oriented Software Development” by R. Filman et al., ISBN: 0321219767

Bru

no H

arbulo

t – E

LF D

evel

oper

s' F

oru

m –

Man

ches

ter

- 19/1

0/0

5

24/24

References (II)

● “Design Pattern Implementation in Java and AspectJ”, by J. Hannemann and G. Kiczales., OOSPLA 2002.

● “Deriving Refactorings for AspectJ”, by L. Cole et al., AOSD 2005.

● “Towards a Catalog of Aspect-Oriented Refactorings”, by M. Monteiro et al., AOSD 2005.