A Meta-Level Specification and Profile for AspectJ in UML

Joerg EvermannSchool of Information Management

Victoria University of Wellington

Yet Another AspectJ Profile?

• Previous work based on UML 1.x– UML 2.x extensions very different– Integrated meta-level extensions– Meta-models are profiles

• Full coverage of AspectJ• Full code generation capabilities• No textual specification or special code

words– Rigorous meta-level based modeling– Supported by all MOF compliant tools

Meta-Level Specification

• CrossCuttingConcern– Not in AspectJ– But important for

modularization– Extend Package meta-

class– Related to Aspect

through the meta-model level

• Aspect– Static features

• Pointcuts

– Dynamic features• Advice

– Generalizable– Similar to meta-model

element Class

Extension Relationships

Aspects

• isPrivileged• declareParents

– Specifies meta-level Generalizations

• declareImplements– Specifies meta-level InterfaceRealizations

• Precedence– Total ordering

• Instantiation– PointCut

Advice• Advices are dynamic

– BehavioralFeature– Expressible as state

charts, collaborations, or opaque behaviour, i.e. methods

• Related to Aspect via meta-model

• Signatures by virtue of Operation

– Subclass of BehaviouralFeature

– Requires behavior specification by method

– Determines when advice is applied (after throwing or after returning value)

Static Crosscutting Features

• Owned by / modelled with the aspect– For better separation of

concerns and encapsulation

– Requires specification of type for introduced features

• Alternative possible– “Cleaner” meta-model

– But less rigorous separation

PointCuts

• Explicit composition– UML has no built-in regular expressions

• Refer explicitly to specific model elements they cut

OCL Constraints

• Advice stereotype only on behavioral features of classes that are stereotyped Aspect

context Advice inv:allInstances.featuredClassifier.oclIsKindOf(Aspect)

• StaticCrossCuttingFeature stereotype only for features of classes that are stereotyped Aspect

context StaticCrossCuttingFeature inv:allInstances.featuredClassifier.oclIsKindOf(Aspect)

• PointCut stereotype only for behavioural features of classes that are stereotyped Aspect

context PointCut inv:allInstances.featuredClassifier.oclIsKindOf(Aspect)

OCL Constraints (2)

• Aspects are either instantiated perPointCut or perType

context Aspect inv: perType->size() > 0 or perPointCut->size() > 0

• Aspect stereotype only on classes packaged in packages that are stereotyped as CrossCuttingConcern

context Aspect inv: package.oclIsKindOf(CrossCuttingConcern)

Code Generation

• AspectJ from XMI• XSLT

– approx 600 lines of code, 9 templates

• Proof of concept– Lacking sufficient error handling

• No support for templated and stereotyped classes (i.e. Java Generics and Annotiations) yet.

• Modeller must ensure advice signature matches context exposed in PointCuts– Not all boolean combinations allowed in AspectJ

Code Generation (2)

• Advice signature (return parameter or raised exception) determines after … returning or after … throwing advice

context Advice inv: if (adviceExecution = AfterAdvice) then

ownedParameter(p |p.direction=return)->size() > 0 or

raisedException->size() > 0

• Different interpretation of return parameter in advice signature– Ignored for before-Advice– Type of returned value for around-Advice– PointCut context for after-Advice

Discussion

• Rigorous Meta-model specification• Lightweight extensions

– Cross-tool support (in theory)

• Lack of pattern based textual specification– Requires awareness of base model– Safer– Easier model verification– No tool support required

Where to from here?

• Two main directions– Breadth: Other AOP languages– Depth: Generic Aspect Profile– Model Transformations for MDA

• Other improvements– Code generation for templated and

stereotyped elements (i.e. Java 5 generics and annotations)

– Validity constraints with OCL– Usability and practical application studies

Thank You