Transcript Eclipse: The universal tools platform

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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 1to-n problem
 Modules are no longer
well defined
Aspect-Oriented Programming in Eclipse
Code View of n-n
Tangled
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”);
}
}
Core Logic
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
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
http://www.eclipse.org/ajdt
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
WSIF for Open
Source Community
org.apache.wsif
+
WebSphere RAS
WebSphere FFDC
WebSphere PMI
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
auxiliary /
exploration
enforcement infrastructure
core /
business
AO Analysis,
AO Design,
AO Strategy
time & confidence
Aspect-Oriented Programming in Eclipse
Further information

AspectJ home page: http://www.eclipse.org/aspectj

AJDT home page: http://www.eclipse.org/ajdt

Pick up a book …

Email us:
 Helen Hawkins: [email protected]
 Sian January: [email protected]