Aspects Every Where

Aspects Everywhere:
Language Extensibility for JDT
through Equinox Aspects

Andrew Eisenberg
AJDT Committer
AspectJ Project

Copyright 2008 SpringSource. Copying, publishing or distributing without express written permission is prohibited.

AJDT is an extension of JDT

Extension
AJDT JDT
of

AspectJ JPython
support for

support for
Groovy And other
Tool

Tool
Scala Java-like
language
JRuby
Extension
AspectJ Java
of
public class Ship {
public aspect ShipAccessor { // ...
// ... }
}

2

A little more about AspectJ

• Aspects
– like classes, but can have pointcuts and
advice
• Pointcuts
– define interesting parts of the (execution of)
program
• Advice
– define extra behavior at interesting parts of
the program
• Weaving (performed by a weaver)
– makes sure advice runs at right time

3

Demo 1

• AJDT 1.6.1
– Provides AspectJ-specific editor
– But does not fully integrate with JDT

4

The problem

• Aspects are
not in Open
Type dialogs

5

The problem

• What I
really want
is this

6

JDT is not really extensible

• The problem runs deep
– Need to plug into JDT's Java model, but can't
– Need to plug into JDT's source indexing, but can't
– Need to plug into JDT's parser, but can't

7

First attempt: Raise a bug!

• Bug 36939: Improve support for Java-like
source files
– Many patches submitted
– 37 votes
– but not resolved
• Outside the scope of JDT

8

Second attempt: eat our own
dogfood!

JDT Weaving Service
• Use AspectJ
– add hooks to JDT
– toggles JDT or extended functionality
• Wrapped in Eclipse extension points
– make extensible to third parties
• Equinox Aspects to support load time
weaving in OSGi environment
• AJDT 1.6.2 and later

9

Demo 2

• AJDT 1.6.4
– Uses JDT Weaving service
– More fully integrated with JDT

10

How does this work?

Uses
AJDT JDT
extension
UI UI
Weaves
points JDT
into
Weaving
JDT
AJDT Service
Core
Core

Other
Load Time bundles...
Weaving class
loading
Equinox &
Aspects OSGi, everything
In is a bundle
extension
support

Equinox-OSGi 11

Equinox Aspects uses AspectJ
weaver

• The weaver is careful which bundles to
touch
• Weaving happens lazily as classes are
loaded
– little effect on startup time
• Once woven, weaver has no more role

12

Example: Plug into JDT's Java
model

• For when it's like Java, but it really isn't
• Need to plug into JDT's Java element
hierarchy
– IJavaElement --- generic Java entity
– ICompilationUnit --- A Java source file
• Objects need to be instantiated at the
right time

13

Example: Plug into JDT's Java
model

1. Define extension:
<extension point=quot;org.eclipse.contribution.weaving.jdt.cuproviderquot;>
<provider class=quot;org.eclipse.ajdt.eclipsecon2009.ShipCUProviderquot;
file_extension=quot;shipquot;/>
</extension>

2. Define compilation unit provider:
public class ShipCUProvider implements ICompilationUnitProvider {
public CompilationUnit create(PackageFragment parent, String name,
WorkingCopyOwner owner) {
return new ShipCompilationUnit(parent, name, owner);
}

14

Demo 3/4

• Simple Ship editor
– Icons
– Searching
– Open type
• Ship Editor source code
– plugin.xml
– Java source code

15

JDT Weaving Service

• JDT functionality is exposed
– AspectJ advice and pointcuts
– exposed as extension points
– no need to be AspectJ aware
– simple and Eclipse-friendly
• Available for download
– with AJDT or separately
http://download.eclipse.org/tools/ajdt/34/update
• Useful for any Java-like language
– Scala Eclipse plugin using this now
16

That's it!

• Links
– AJDT : http://eclipse.org/ajdt
– Equinox Aspects :
http://www.eclipse.org/equinox/incubator/aspects/index.php
– Source code and more implementation details :
http://contraptionsforprogramming.blogspot.com
– AspectJ in Action by Ramnivas Laddad available at bookstore

17

CompilationUnitProviderAspect

pointcut compilationUnitCreations(PackageFragment parent,
String name, WorkingCopyOwner owner) :
call(public CompilationUnit.new(PackageFragment,
String, WorkingCopyOwner)) &&
args(parent, name, owner);

CompilationUnit around(PackageFragment parent,
String name, WorkingCopyOwner owner) :
compilationUnitCreations(parent, name, owner) {

String fileExtension = findFileExtension(name);
ICompilationUnitProvider provider =
CompilationUnitProviderRegistry.getInstance()
.getProvider(fileExtension);
if (provider != null)
return provider.create(parent, name, owner);
return proceed(parent, name, owner);
}

18

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