CSC450 Software Engineering

Devon M. Simmonds University of North Carolina, Wilmington Introduction to AspectJ CSC450Software Engineering

Outline • Quick review • Introduction to AspectJ • Aspects • Pointcuts • advice • Intertype declarations • Money transfer example aspect • Review & Summary

A Quick Review What are Concerns? • Something that is of interest to a stakeholder, • Functional • Non-functional • Security, reliability, performance 3

A Quick Review Cross-cutting concerns • Cross-cutting concerns are concerns whose implementation cuts across a number of program components. • Scattering – code for one feature appears in multiple modules • Tangling – code in one module addresses multiple concerns

A Quick Review Cross-cutting concerns logging is not modularized • Cross-cutting concerns are concerns whose implementation cuts across a number of program components. • Scattering – code for one feature appears in multiple modules • Tangling – code in one module addresses multiple concerns

Aspect-Oriented Software Development (AOSD) • Aspect-oriented software development (AOSD) is an approach to software development that supports the systematic identification, separation, representation and composition of crosscutting concerns. • In AOSD crosscutting concerns are encapsulated in modules known as aspects. 6

AspectJ • AspectJ is an implementation of aspect-oriented programming for Java. AspectJ Java Package Pointcut Class Advice Aspect Intertype Declarations Variables Variables Methods Methods

Java • AspectJ non-Java concepts • Pointcut- An AspectJ statement that identifies join points and values at those points. • Join point - a well-defined point in the program flow, e.g., a method call. • Advice - A piece of code that is executed when a join point is reached. • Inter-type declarations – AspectJ statements for modifying a program's static structure, namely, the members of its classes and the relationship between classes. • Aspect - The AspectJ unit of modularity for crosscutting concerns and may also include pointcuts, advice and inter-type declarations. Aspect AspectJ Package Pointcut Class Advice Intertype Declarations Variables Variables Methods Methods

The HelloWorld Aspect public class Test { public void helloWorld() { System.out.println(“Hello World”); } public static void main(String[] args){ Test test = new Test(); test.helloWorld(); } }//end of class public aspect TestAspect { pointcutoutputLog() : call(public void helloWorld() ); before() : outputLog() { System.out.println(“before call”); } }//end of aspect

Specifying AspectJ Join Points • Method call join point: call(MethodPattern) • Picks out each method call join point whose signature matches MethodPattern, e.g. call(public void helloWorld()). • Method execution join point: execution(MethodPattern) • Picks out each method execution join point whose signature matches MethodPattern, e.g., execution(public void helloWorld()). • Variable reference join point: get(FieldPattern) • Picks out each field reference join point whose signature matches FieldPattern, e.g., get(double balance). • Variable set join point: set(FieldPattern) • Picks out each field set join point whose signature matches FieldPattern, e.g., set(double balance).

Some AspectJ Pointcuts • Variable use join point: withincode(MethodPattern) • Picks out each join point where the executing code is defined in a method whose signature matches MethodPattern, e.g., withincode(public void deposit(double)). • Variable use join point: cflow(Pointcut) • Picks out each join point in the control flow of any join point P picked out by Pointcut, including P itself, e.g., cflow(P1 ) || cflow(P2)). • etc.

Join Point States • Each join point potentially has three pieces of state associated with it: • the currently executing object • the target object • an object array of arguments. • These are exposed by the three state-exposing pointcuts: • this, target, and args, respectively.

Pointcuts for Join Point States • this(Type or Id) • Picks out each join point where the currently executing object (the object bound to this) is an instance of Type, or of the type of the identifier • target(Type or Id) • Picks out each join point where the target object (the object on which a call or field operation is applied to) is an instance of Type, or of the type of the identifier Id . • args(Type or Id, ...) • Picks out each join point where the arguments are instances of the appropriate type (or type of the identifier if using that form). Pointcuts may be composed with boolean operators (&&, ||, !) to build up other pointcuts.

Example 1: A FigureElement UML Diagram FigureElement <<Factory>> Figure Display • Identify each point where the setX method in Point is called. • call(void Point.setX(int)) • Identify each point where the setX method in Point is executed. • execution(void Point.setX(int)) • What join points does this statement pick out? • call(void Point.setX(int)) || call(void Point.setY(int)) +setXY(int, int) +setX(int) +setY(int) +draw() +makePoint () +makeLine() Point Line -x: int -y: int -p1: Point -p2: Point

Pointcut Example • General pointcut format: • pointcutpointcut-name (parameters) :designator ; • pointcut move(): call(void FigureElement.setXY(int,int)); • pointcut move(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int));

Aspect with Pointcut • aspect TestPointcut { pointcut move(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int)); } Name-based crosscutting

Property-based Pointcuts • AspectJ also provides mechanisms that enable specifying a pointcut in terms of properties of methods other than their exact name. • E.g. using wildcards in certain fields of the method signature. • call(void Figure.make*(..)) • picks out calls to the factory methods makePoint and makeLine.

Advice • Pointcutsonly pick out join points. To actually implement crosscutting behavior, we use advice. • Advice brings together a pointcut (to pick out join points) and a body of code (to run at each of those join points). • Advice in AspectJ • Before advice • runs as a join point is reached, before the program proceeds with the join point. For example, before advice on a method call join point runs before the actual method starts running, just after the arguments to the method call are evaluated.

Aspect with before Advice • aspect TestPointcut { pointcutmove(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int)) || call(void Line.setP1(Point)) || call(void Line.setP2(Point)); before(): move() { System.out.println("about to move"); } }

After Advice • After advice runs after code at the join point . • After advice on a method call join point runs after the method body has run, just before control is returned to the caller.

Aspect with before Advice • aspect TestPointcut { pointcutmove(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int)); after(): move() { System.out.println("just successfully moved"); } }

Around Advice • Around advice on a join point runs as the join point is reached, and has explicit control over whether the program proceeds with the join point.

Aspect with around Advice • aspect TestPointcut { pointcutmove(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int)) || call(void Line.setP1(Point)) || call(void Line.setP2(Point)); void around(): move() { System.out.println(“no method executed"); } }

Aspect with around Advice • aspect TestPointcut { pointcutmove(): call(void FigureElement.setXY(int,int)) || call(void Point.setX(int)) || call(void Point.setY(int)) || call(void Line.setP1(Point)) || call(void Line.setP2(Point)); void around(): move() { //do something proceed(); } }

Join Point Context • A pointcut declaration has a parameter list that can be used to expose variables defined at the join points. • Values exposed by a pointcut can be used in the body of advice declarations. • An advice declaration has a parameter list (like a method) that gives names to all the pieces of context that it uses.

Outline • Quick review • AOSD terminology • Introduction to AspectJ • Aspects • Pointcuts • advice • Intertype declarations • Money transfer example aspect • Summary

Intertype Declarations • AspectJ's mechanisms for modifying classes and their hierarchy by: • introducing or inserting new code into a target class of an application, • changing the inheritance or interface hierarchy of a class or collection of classes. • Compared to advice which is generally dynamic, introductions are static and are executed at compile time.

Intertype Declarations • Examples • Adding variables private Address Account.address; private String MoneyTransferService.serviceName; • Adding methods public void Account.changeAddress(Address newAddress){ //… }

Intertype Declarations • Changing the inheritance hierarchy declare parents: Account implements NewAccount; declare parents: StockClient extends Frame; <<Interface>> NewAccount Frame Account StockClient

A Money Transfer Example Client • Problems: • Initiate a transaction each time a money transfer begins. Close the transaction when the money transfer ends. • Problem 2: Cancel the transaction and charge a fee of 1% of the transfer amount, if the source and target accounts of a money transfer are the same Account deposit(double amt) withdraw(double amt) 1..* 1..* requests manages MoneyTransferService 1 1..* moneyTransfer(a:Account, b:Account, amount:double) Info(info:String)

MoneyTransferService.java package MoneyTransfer; import java.lang.*; import java.io.*; public class MoneyTransferService { Account acc1, acc2; public MoneyTransferService () { System.out.println("\nMoneyTransferService object created"); } public void moneyTransfer (Account a1, Account a2, double amount) { a1.withdraw(amount); a2.deposit(amount); } public void info (String str) { System.out.println( "MoneyTransferService: " + str ); } }

Client.java package MoneyTransfer; import java.lang.*; import java.io.*; public class Client { public static void main(String[] args) { Account acc1, acc2; try { MoneyTransferService service = new MoneyTransferService(); acc1=new Account(“Tammy", 12345, 400); acc2=new Account(“Jason", 12346, 375); service.moneyTransfer(acc1, acc2, 200); acc1.deposit(444); } catch(Exception e) { e.printStackTrace(); } } }

MoneyTransferServiceAspect.java package MoneyTransfer; import java.lang.*; import java.io.*; import java.util.*; public aspect MoneyTransferServiceAspect { //Problem 1: Initiate transaction when money transfer begins / Close transaction when money transfer ends. pointcut manageTransaction(MoneyTransferService s, Account acc1, Account acc2, double amount): execution(public void moneyTransfer(Account, Account, double)) && target(s) && args(acc1,acc2,amount); before (MoneyTransferService s, Account acc1, Account acc2, double amount): manageTransaction(s,acc1,acc2,amount) { try{ s.info("Transaction initiated..."); }catch(Exception e){} } after(MoneyTransferService s, Account acc1, Account acc2, double amount): manageTransaction(s,acc1,acc2,amount) { try{ s.info("Transaction committed..."); }catch(Exception e){} } }//end of aspect

MoneyTransferServiceAspect.java package MoneyTransfer; import java.lang.*; import java.io.*; import java.util.*; public aspect MoneyTransferServiceAspect { //Problem 2: Cancel the transaction and charge a fee of 1% of the transfer amount, if the source and target accounts of a money transfer are the same pointcut cancelTransaction(MoneyTransferService s, Account a1, Account a2, double amount): execution(public void moneyTransfer(Account, Account, double)) && target(s) && args(a1,a2,amount); void around(MoneyTransferService s, Account a1, Account a2, double amount): cancelTransaction(s,a1,a2,amount) { try{ if(a1.getAccNumber() == a2.getAccNumber()) { System.out.println("=== Calcellation fee will be charged ..."); a1.withdraw(amount*0.01); } else proceed(s,a1,a2,amount); }catch(Exception e){} }}//end of aspect

Review: AOSD Terminology • Aspect – • a program abstraction that encapsulates a crosscutting concern. • Join point – • an event in an executing program where crosscuting code may be executed. • Advice – • the (crosscutting) code executed at a join point • Pointcut – • a statement included in an aspect that defines the join points where the associated aspect advice should be executed. • Join point model – • the set of events that may be referenced in a pointcut. • Weaving – • incorporating aspect advice at specified join points by an aspect weaver.

Summary • Crosscutting concerns • AOSD using AspectJ • Aspects • Pointcut, advice, intertype declaration • A complete example with compilation instructions • LINK

Resources • The AspectJ web site is: http://www.eclipse.org/aspectj/ • You can download the latest stable release of AspectJ 5 (1.5.3) from http://www.eclipse.org/aspectj/downloads.php • You can find information about the language in the Programmers Guide: http://www.eclipse.org/aspectj/doc/released/progguide/index.html • The Quick Reference is also an excellent guide to the language syntax: http://www.eclipse.org/aspectj/doc/released/quick5.pdf • Compilation instructions may be found in the Development Environment Guide and the ajccompiler page: http://www.eclipse.org/aspectj/doc/released/devguide/ajc-ref.html

Qu es ti ons? The End ______________________ Devon M. Simmonds Computer Science Department University of North Carolina Wilmington _____________________________________________________________

CSC450 Software Engineering

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