Dean Wampler's Mind

Raising a different exception in "after" or "after_raising" advice

2008-04-26T16:13:04-05:00

An Aquarium user asked recently if you can use after_raising advice to raise a different exception, e.g., to wrap the original exception. Now you can, with the commits I did today. (This change will appear in the forthcoming V0.4.2 release.) Actually, this feature was partially implemented already, but never finished (OOPS!)

The following made-up example illustrates what you can do. Imagine you are one of the handful of Ruby programmers who aren’t using ActiveRecord ;) and you have an OracleDriver class that handles Oracle database transactions.


class OracleDriver
  class OracleDriverException < StandardException; ...; end
  class ConnectionError < OracleDriverException; ...; end
  def connect
    if try_to_connect == false
      raise ConnectionError 
    end
    ...
  end
  def find query_parameters
    ...
  end
end

In the application code that uses the OracleDriver you ignore any exceptions raised (because we will implement an exception handling strategy elsewhere…).


  ...
  def load_object oracle_driver, query_parameters
    oracle_driver.connect
    oracle_driver.find query_parameters
  end
  ...

Finally, you implement an application-wide exception handling strategy for any exceptions raised by the driver.


Aspect.new :after_raising => OracleDriverException, 
    :in_types => ... do |jp, object, *args|
  # Ruby needs a standard way to wrap one exception in another.
  original = jp.context.raised_exception
  app_exception = ApplicationException.new(original.message)
  app_exception.set_backtrace(original.backtrace)
  jp.context.raised_exception = app_exception
end

In other words, any exceptions raised by calls to OracleDriver are wrapped in an ApplicationException, which will be thrown by Aquarium when the advice block finishes.

This technique can also be used when handling exceptions in after advice.

By the way, in a similar way, you can also change the return value in after and after_returning advice. In this case, you assign a new value to jp.context.returned_value.

Short presentation Aquarium

2008-04-03T04:37:23-06:00

I just posted the PDF for a short (30 minute) presentation on Aquarium that I presented to the aspect-oriented programming research community at the Aspect-Oriented Software Development 2008 Conference. It assumes some familiarity with aspects, but not much experience with Ruby. The talk was based on my Industry Track paper.

There is a longer presentation on Aquarium on my papers page, which is better if you are new to AOP (although the syntax shown in the Aquarium examples is a bit dated…).

ANN: Aquarium V0.4.0 Released with Initial Support for Java Aspects in Aquarium

2008-02-26T12:12:25-06:00

The new V0.4.0 release of Aquarium adds support for JRuby. Not only do the regular “pure Ruby” Aquarium specs run reliably under JRuby (V1.1RC2), but you can now write aspects for Java types with Aquarium!

There are some limitations and issues. For details, see my blog at Object Mentor and the JRuby page at the Aquarium website.

ANN: Aquarium V0.3.0 released

2008-01-21T13:38:00-06:00

I released V0.3.0 of Aquarium today. The most visible change is a new set of synonyms for many of the parameters passed to API methods, providing a more “English-like” feel. For example, previously, you might declare an aspect like this:

around :methods => :all, :types => [Foo, Bar], :advice => advice_proc

Now you can write the same aspect as follows:

around :calls_to => :all_methods, :within_types => [Foo, Bar], :use_advice => advice_proc

which reads more like English.

Similarly, attribute matching is simpler.

after :attribute => name, :attribute_options => [:readers], :objects => [foo, bar] ...

becomes

after :reading => name, :on_objects => [foo, bar] ...

There are many internal improvements to improve DRY’ness, robustness, and performance.

There should be no upgrade issues, so give it a try!

CJUG Downtown 12/18/07: Aspect-Oriented Programming and Software Design

2007-12-08T12:02:14-06:00

I’m reprising my CJUG West talk on Aspect-Oriented Programming and Software Design in Java and AspectJ for the downtown Chicago group on December 18th.

I will briefly describe the problems that AOP addresses and how the principles of object-oriented design influence AOP and vice versa. If you’re in the area, I hope to see you there.

Presentation on AOP in Academia and Industry

2007-10-20T20:50:00-05:00

Yesterday evening, I gave a talk on AOP at DePaul University called Aspect-Oriented Programming in Academia and Industry. Here’s the PDF.

This talk was a little different than the usual talks I give. Since this audience was mostly students and faculty, I wanted to show how groups in both industry and academia were looking at similar problems that led to the emergence of AOP, how they each contributed to AOP in different ways, and how they can continue complementing each other’s work on emerging trends, like Language-Oriented Programming.

Language-Oriented Programming is not a new idea, but it is getting renewed attention recently. I see it as a way of formalizing our understanding of how Domain-Specific Languages should be designed.

I’m a little concerned that everyone will get so excited about crafting “elegant” DSLs that we’ll end up with a Tower of Babel situation; lots of gratuitously-different ways of describing the same thing and no one getting much work done.

Anyway, we’ll see…

Presentation on Aquarium with Exercises

2007-10-02T14:06:00-05:00

I’ve posted a PDF for the presentation I did last night on Aquarium at the Chicago Ruby Users Group (Chirb).

I also posted a zip file with three exercises that are adapted from the examples on the aquarium web site.

Speaking at the Chicago Ruby Users Group (Chirb)

2007-09-29T08:30:28-05:00

I will give a presentation on Aquarium at Chirb this Monday evening, Oct. 1st. David Chelimsky will also be speaking on new developements in RBehave and RSpec. Details are here.

David and I will be doing a joint presentation at the December meeting. It will be a tutorial on Ruby metaprogramming.

ANN: Aquarium v0.1.5 released

2007-09-17T21:15:00-05:00

This is primarily a bug-fix release. I labeled it “v0.1.5” instead of “v0.1.1”, because a non-trivial API change was required; Aquarium no longer automatically adds methods to Object, due to collisions with Rails. This means that users of the “DSL methods” will need to require a new file or include a new module.

See the “CHANGES” file in the distribution of here for more information.

ANN: Contract4J5 V0.8.0 Released

2007-09-13T11:19:38-05:00

I just released V0.8.0 of Contract4J5. This release deprecates support for JRuby (for reasons discussed in the README) and provides general robustness improvements, especially in the area of test expression evaluation.

My plan is to complete all the remaining “1.0” features by the 0.9 release towards the end of the year. I hope to (finally) release 1.0 early next year.

Please visit the Contract4J web site for more information.