Monday, March 05, 2007

Reflective Revolution...

It has been interesting to see the evolution of the use of reflection. I think, though I may be wrong that it was java that was the first platform to fully support reflection. At that stage I'm not sure the developers of java realised what it would become. The birth and subsequent development of a technology often follows this pattern. It starts off as a feature which might be used in one or two rare situations, as it gains traction and support, and most important performance, it moves into more mainstream applications.

In recent times, probably the last 5 or 6 years, reflection has become central to so many applications. One of the original uses of reflection was java serialization, The poster boy of reflection is probably Struts. Translating an http form submission and populating the relevant java form would not be possible without reflection.

Many more applications were found for reflection to add value for instance, it significantly simplifies runtime enacted AOP and makes is essential component in the development of rich object relational mapping tools available on the java platform.

I can hear the reader asking about performance... let me acknowledge that yes, certainly historically that has been a factor, but I think the java brains trust have expended much resources improving this situation. Each edition of the java runtime has seen significant improvements in performance of reflection such that in 1.6 the performance penalty is negligible. In 1.3 it was slow, in 1.4 is was adequate, 1.5 brought it up to reasonable pace and 1.6 has further improved on this. It is slower than direct method calls whichever VM is used, but the value that it adds more than makes up for the performance penalty. The old adage that says, design first, and then optimise later applies. Because the performance penalty introduced with reflection is constant, in reality it will probably not be the biggest culprit.

Reflection probably has an even greater contribution to make to modern programming. It is probably fair to say that developers do not consider using it. Performance will probably play a role here, but also a loss of explicitness. The code is not as self explanatory, errors may only appear at runtime for instance. There are applications where this loss of explicitness is not as much of a factor.

For instance, on our project we require the ability to copy between context, from dto's to model objects. Reflection is a useful tool in this case. When needing to update a data managed object with a dto object. Another useful non invasive use of reflection is to compare two objects for testing purposes. There are probably a number of factors to look at when considering using reflection...

1.Does the solution to the problem require much repetitive “dog work” code.
Copying values from one object to another is the bread and butter of reflection. The bean utils library is a useful addition to a developers arsenal in this respect.
2.Will the reflective element be executed many times
One of relection's biggest value adds is that can replace hand written functionality and modularise it. If you can solve a task with reflection you can reduce the amount of hand written code required and thus increase the quality. The more hand written code there is, the more bugs there will be.

What is interesting about the current situation in the project is that speed of development has become the driving force behind everything. We have got to speed up the process. Reflection is a particularly useful arrow in the quiver in this regard.