RE: [aspectj-users] Help with a Dependency Passing Aspect

["Ron Bodkin" <rbodkin@xxxxxxxxxxxxxx>]

Hi Matt,

How is foo associated with the method anotherExample? It's not defined on
Foo in the example. Could you extend your approach to also initialize the
Bar types that are created via FooBarFooFactory, by accessing Bar.getRoot()?

-----Original Message-----
From: aspectj-users-bounces@xxxxxxxxxxx
[mailto:aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Matt Kendall
Sent: Thursday, May 17, 2007 9:19 AM
To: aspectj-users@xxxxxxxxxxx
Subject: [aspectj-users] Help with a Dependency Passing Aspect

I've been trying to figure out this aspect for the past few hours.
Hopefully someone can help since I'm new to AOP. I'm working on a
project where I have several Foo objects that are the root of object
graphs. The members of each Foo graph need to access Foo on a regular
basis, but they need to access the Foo to which they belong (not a
global singleton). If I wanted to maintain a whole lot of extra code,
I'd write something like this to accomplish what I want:

class Foo {
  public FooBar getSomeResource() {
    return someResource;
  }
  public Bar anExample() {
    Bar bar = BarFactory.createABar(this); // Creates and returns a Bar
                                                             // that
has a reference to this Foo.
    return bar;
  }
}

class Bar {
  private Foo root;
  public Bar(Foo root) {
    this.root = root;
  }
  public FooBarFoo anotherExample() {
    return FooBarFooFactory.createAFooBarFoo(root);
  }
}

Hopefully that makes some amount of sense. My original tactic, which
worked quite well at first, was to use the following aspect:

public aspect FooInitializer {
  pointcut withinFoo(Foo foo): within(Foo) && this(foo);
  pointcut initialize(FooWorker bar, Foo foo):
initialization(FooWorker.new(..)) && target(bar) &&
cflow(withinFoo(foo));
    before(FooWorker bar, Foo foo): initialize(bar, foo) {
    bar.initialize(foo);
  }
}

Basically, any class that needed an instance of Foo in order to do its
work just implemented the FooWorker interface and the dependency was
injected. Unfortunately, that aspect won't work if a member object of
Foo escapes its cflow. For example, using the code from above:

Foo foo = new Foo();
Bar bar = foo.anExample();
FooBarFoo fbf = foo.anotherExample(); // Will not be initialized
because it wasn't
                                                         // created in
the cflow of Foo.

So, what I'm looking for is a way to *pass* a dependency to any object
created by an object that knows about said dependency. Note that I
cannot just look for calls
to constructors directly, since the member object may be created in a
factory or the database layer.

Hopefully that makes some sort of sense. Thanks for reading!
Matt
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