Aspect-Oriented Programming

Aspect-Oriented Programming Andrey Bratukhin, 2011

Contents
Introduction
Main conceptions in AOP
AspectJ as one of implementation
Pointcuts in AspectJ
Advice in AspectJ
Inter-type declaration
Weaving
Bad practicies
Conclusion

Introduction
Gregor Kiczales and colleagues at Xerox PARC developed the explicit concept of AOP, and followed this with the AspectJ AOP extension to Java.
Aspect-oriented programming is a way of modularizing crosscutting concerns much like object-oriented programming is a way of modularizing common concerns.

Motivation void transfer ( Account fromAcc, Account toAcc, int amount, User user, Logger logger ) throws Exception { logger.info ( "transferring money..." ); if (! checkUserPermission ( user )){ logger.info ( "User has no permission." ); throw new UnauthorizedUserException (); } if ( fromAcc.getBalance () < amount ) { logger.info ( "Insufficient Funds, sorry" ); throw new InsufficientFundsException (); } fromAcc.withdraw ( amount ); toAcc.deposit ( amount ); //get database connection //save transactions logger.info ( "Successful transaction." ); }

Tangled code

Dispersed code Module #1 Module #1 Module #1 Security API calls Security module

Extract common concerns Module #1 Module #1 Module #1 Automated integration of calls Security module Security aspect

Main concepts of AOP
JoinPoint are points in a running program where additional behavior can be usefully joined.
Pointcut is a way to specify (or quantify) join points.
Advice is the code to run at a join point.
Inter-type decoration provide a way to express crosscutting concerns affecting the structure of modules.
Weaving is the process of applying aspects to code.

AspectJ example public aspect SomeAspect { pointcut allMethodCalls () : call (* *.*(..)); before () : allMethodCalls () { Logger.log ( "Before " + thisJoinPoint .toLongString ()); } after () : allMethodCalls () { Logger.log ( "After " + thisJoinPoint .toLongString ()); } }

Join points
Method or constructor execution
Method or constructor call
Read/write field
Handling of exceptions
Initialization of class and objects

Pointcuts Signature Example *, .., + call(public *.new(int)), call(public Account.new(..)), execution(public Account+.new(..)) &&, ||, ! call(* int Account.*(..)) || call(* double Account.*(..)) && !within(Account) call(Signature), execution(Signature) call(public *.new(int)), execution(public Account+.new(..)) get(Signature), set(Signature) get(* System.out), set(private Account.amount) handler(TypePattern) Handler(* Account) within(TypePattern), withincode(Signature) within(* Account), withincode(private Account.transfer(..)) staticinitialization(TypePattern) staticinitialization(* Account)

Advice
before(Formals) – runs before each join point.
after(Formals) returning – runs after each join point that returns normally.
after(Formals) throwing – runs after each join point that throws a Throwable.
after(Formals) – runs after each join point regardless of whether it returns normally or throws a Throwable.
Type arround(Formals) – runs in place of each join point.

Inter-type declaration declare parents : Account implements Serializable ; declare @type : Account : @MyAnnotation ; private String Account.name ; private void Account.getName ( String name ) { this .name = name ; } private String Account.getName () { return name ; } declare warning : get (* System.out ) && ! within ( Logger ) : "Use Logger.log()" ;

Weaving
Source-to-source weaving
Post-compile weaving
Load-time weaving
Dynamic Proxy

Bad practicies
Aspect for single class or method
Business logic strongly depends on aspects
Duplicating of functionality of runtime environment (EJB, OSGi and etc.)
Aspect hides valuable functionality of application
No unit or integration tests

Alternatives
Frameworks
Runtime environments
Codegeneration
Design patterns:
Observer
Chain of responsibility
Decorator
Proxy
etc.

Aspect-Oriented Programming

by Andrey Bratukhin on Mar 28, 2011

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