Aspect Oriented Programming

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Aspect Oriented Programming

• Sumathie Sundaresan
• CS590 Summer 2007
• June 30, 2007

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Background
Procedural Languages like Fortran, Pascal, C
Object Oriented Programming like Java, C
Aspect Oriented Programming Frameworks like
AspectJ etc.
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Advantages of OOP

• Modularity
• Reduce large problems to smaller
• Reusability
• Inheritance
• Polymorphism
• Reliability
• Robustness
• Maintainability
• Extendibility

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Problems with OOP

• Not much strong reusability of code
• Every time inherit one base class
• Or Use delegation
• A functional unit can not be isolated, even they
  crosscut programs at many places
• Logging, security checks, transaction management
• Crosscutting concerns increases the cost of
  developing and maintenance cost.

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Introduction

• Aspect Oriented Programming
• Was discovered in Palo Alto Research Center
  during 1980s and 1990s
• Is to Object Oriented Programming (like C to
  C)?
• Does not replace Object Oriented Programming
  technique, it complements it
• Is a technique
• Allows programmers to modularize the crosscutting
  concerns
• Separate crosscutting concerns from an
  application

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Terminology

• Aspect
• Is a unit of modularity, encapsulation and
  abstraction
• Is like a class in object oriented technology
• Can be used to implement crosscutting concerns in
  a modular fashion
• Summarize behaviors that affect multiple classes
  into reusable modules
• Cross-cutting concerns
• Find out certain behavior to occur at one or more
  points in a program

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Cont'd.....

• Join Points
• Identify the points in the execution of
  components where aspect should be applied
• For example execution of method constructor

referred from www.cs.umd.edu
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Cont'd.....

• Pointcuts
• Used to select join points
• Advice
• Specifies what to do at joint points
• For example
• Before(...) PointcutExpr(...)
• After(...) PointcutExpr(...)
• Around(...) PointcutExpr(...)
• Weaving
• Task which is done by compiler in linking classes
  and aspect together
• Is no longer needed if there is an aspect
  oriented compiler available.

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Example

• package hello
• public class HelloWorld
• public void sayHello()
• System.out.println("Hello")
• public static void main(String args)
• new HelloWorld().sayHello()
• public aspect World
• pointcut greeting()
• execution( HelloWorld.sayHello(..))
• after() returning greeting()
• System.out.println("World!")

Join Point
Advice
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AOP tools in Java

• AspectJ(we are using this)?
• JBOSS AOP
• Spring AOP
• JAC

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Installing AspectJ

• Command line
• Download AspectJ from aspectj.org
• Start the installation by running java-jar
• java jar aspectj-1.5.3.jar
• Setup path and classpath
• Compile AspectJ programs by
• ajc YourJavaClass.java YourAspect.aj
• gtajc Hello.java World.aj
• Eclipse
• http//www.eclipse.org/ajdt/downloads/
• Get the ajdt_1.4.1_for_eclipse_3.2 zip file
• Extract the zip file in to the eclipse folder
• http//www.eclipse.org/aspectj/doc/next/runtime-ap
  i/index.html

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What is AJDT?

• AspectJ Development Tools
• Comprehensive tool support for using AspectJ in
  Eclipse
• Integrating the AspectJ compiler
• New editors/views/wizards for working with
  AspectJ artefacts
• Tool support is critical for AOP
• For day to day development of AO programs
• For learning AO concepts and understanding the
  power of AO

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The outline view

• Shows aspect structure post compilation
• Advice
• Inter-type declarations
• Declared warnings/errors
• Defined Pointcuts
• Useful feedback loop
• Did my pointcut match anything?
• Fully navigable
• Jump to advised locations

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Source Annotations

• Gutter annotations in editor view
• Highlight lines affected by advice
• Hover help shows advice in affect
• Context menu for annotations allows navigation to
  advice
• Important visual cue for developers
• Not all users have the outline view active

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Aspect Visualizer

• Shows scattering, tangling, crosscutting
• SeeSoft style
• Optionally
• Look at affect of particular aspects
• View at the package or class level
• Navigate from affected lines back to source
• Even zoom in !

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Good Modularity URL Pattern Matching

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

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Problems Logging is not modularized

• instances of logging in org.apache.tomcat
• red represents lines of code that handle logging
• occurences are not in just one place, and
• in a significant number of places

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Summary Purpose of AOP

• AOP is an extension of OOP
• AOP does not replace OOP
• AOP has functions, classes and aspects
• Make design and code more modular
• Isolate the concerns for separate development
• Separate expression of behavioral concerns from
  structural ones
• Poor composition can lead to interference

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The Future of AOP

• Language Design
• Standardization across frameworks
• Tool Development
• IDE support, UML support, aspect discovery,
  re-factoring, re-cutting, source level debuggers
• Dynamic Source Weaving (Wicca - debugs
  dynamically composed aspect-enabled programs)?
• Software Engineering
• Finding aspects that help define modularity in
  aspects
• Concern Manipulation Environment (CME)
• Open source Eclipse project targeting AO
  technologies
• Theory
• Consistency in varying compiler interpretation
• Fast compilation
• Advanced crosscut constructs

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Thank you!

• Questions?