Aspect-Oriented Programming In Eclipse ® Aspect-Oriented Programming in Eclipse with AspectJ Dr Helen Hawkins and Sian January

Aspect-Oriented Programming in Eclipse Outline  The need for Aspect-Oriented Programming (AOP)  An introduction to AspectJ  AspectJ Demos  Adopting AOP  Further information

Aspect-Oriented Programming in Eclipse The 1-to-1 idea: Good modularity  One requirement in your design maps to one module in your implementation  For example – Chess Piece, Chess Board, Player  Clear, simple, direct mapping  Modules are  easy to add  easy to remove  easy to maintain

Aspect-Oriented Programming in Eclipse The 1-to-1 idea: Good modularity  Socket Creation in Apache Tomcat  Red shows the relevant lines of code  Nicely fits into one package – 3 classes

Aspect-Oriented Programming in Eclipse When things go wrong…  Logging in Tomcat  Scattered and tangled throughout all the packages  Bad Modularity – 1-to-n mapping

Aspect-Oriented Programming in Eclipse The trouble with 1-to-n  Redundant code  Same fragment of code in many places  e.g. trace.entry(); trace.exit();  Difficult to understand  Mapping from the requirement is unclear  Structure is not explicit  Difficult to change  Have to find all the code involved  And be sure to change it consistently  And be sure not to break it by accident

Aspect-Oriented Programming in Eclipse n-to-1 and n-to-n  A consequence of the 1- to-n problem  Modules are no longer well defined

Aspect-Oriented Programming in Eclipse Code View of n-n try { if (!removed) entityBean.ejbPassivate(); setState( POOLED ); } catch (RemoteException ex ) { FFDCEngine.processException( ex,”EBean.passivate()”,”237”, this); destroy(); throw ex; } finally { if (!removed && statisticsCollector != null) { statisticsCollector. recordPassivation(); } removed = false; beanPool.put( this ); if (Logger.isEnabled) { Logger.exit(tc,”passivate”); } try { if (!removed) entityBean.ejbPassivate(); setState( POOLED ); } catch (RemoteException ex ) { destroy(); throw ex; } finally { removed = false; beanPool.put( this ); } Example: Code to handle EJB Entity bean passivation Tangled Core Logic

Aspect-Oriented Programming in Eclipse Aspect-Oriented Software Development …  Recognises crosscutting concerns:  Are inherent in any complex system  Have a clear purpose  Have a natural structure  Captures crosscutting concerns explicitly:  In a modular way  With linguistic and tool support

Aspect-Oriented Programming in Eclipse AspectJ  An aspect oriented programming (AOP) language  Java language extension  Divides system into  core concerns (classes)  crosscutting concerns (aspects)  Broad IDE support  Eclipse, Emacs, JBuilder, NetBeans, …

Aspect-Oriented Programming in Eclipse AOP Concepts  Join points  Pointcuts  Advice  Aspects

Aspect-Oriented Programming in Eclipse Join Points  Events in the execution of a program  Types of Join Points :  Method & Constructor call  Method & Constructor execution advice execution  Field get & set  Exception handler execution  Static & dynamic initialization

Aspect-Oriented Programming in Eclipse What’s a Pointcut?  Pointcut  Picks out join points in a particular system  e.g. call of method ‘foo()’, set of field ‘x’, constructor for object ‘Fred’  Can also expose context from the matched join point

Aspect-Oriented Programming in Eclipse Types of Pointcuts  Event based - well defined execution points, e.g.  method calls, executions  field gets / sets  exception handling  object and class initialisation  Scoping - only select join points within a certain scope, e.g.  within a set of packages,  within the implementation of a method,  in the control flow of some event (e.g. downstream of an unsecured call)  Context matching - expose context at the join point, e.g.  identity of the caller or target object  exception being handled  value being put into a field

Aspect-Oriented Programming in Eclipse What’s Advice?  Java code to execute when conditions of a pointcut are met.  Can be parameterized to process context exposed by the pointcut

Aspect-Oriented Programming in Eclipse Types of Advice  before()  Executes before the join point  after() throwing/returning  Executes after the join point, execution can be made conditional on how join point exits (i.e. with/without exception)  around()  Executes ‘instead of’ the join point – has a choice about whether to invoke the original logic

Aspect-Oriented Programming in Eclipse What is an Aspect?  Aspects are...  At the design level … concerns that crosscut  At the implementation level … a programming construct Aspect = pointcut + advice

Aspect-Oriented Programming in Eclipse Demos – AJDT  AspectJ Development Tools (AJDT) for Eclipse  Open Source  Developed in Hursley  Partnership with AspectJ team 

Aspect-Oriented Programming in Eclipse Demos  Demo 1: A Simple Figure Editor  Demo 2: Web Services Invocation Framework

Aspect-Oriented Programming in Eclipse Web Services Invocation Framework (WSIF)  Middleware component  Simple Java API for invoking web services, no matter how or where they are provided  Released to Apache  But IBM wants a version tightly coupled to IBM’s normal ‘qualities of service’ IBM tracing/monitoring/management  How do we manage this?

Aspect-Oriented Programming in Eclipse Exploring Re-Use: The WSIF Story org.apache.wsif WebSphere RAS WebSphere FFDC WebSphere PMI + WSIF for Open Source Community Composition WSIF for WebSphere

Aspect-Oriented Programming in Eclipse Applications of AOP  Problem determination  Logging, FFDC, performance monitoring  Architectural rule enforcement  Contracts, encapsulation, separation (no “up calls”)  Other concerns  Security, transactions, persistence, caching/pooling, locking  Open source integration

Aspect-Oriented Programming in Eclipse Adopting AOP reward time & confidence auxiliary / infrastructure core / business AO Analysis, AO Design, AO Strategy exploration enforcement

Aspect-Oriented Programming in Eclipse Further information  AspectJ home page:  AJDT home page:  Pick up a book …  us:  Helen Hawkins:  Sian January: