One might argue that in a container based system that will eventually support clustering and scalability doesn't have to worry about savoring individual CPU cycles that might be expended needlessly with a reflection-based design. Just add more hardware and the user experience will be perpetually preserved. I would argue, however, that the development community will be able to make better use of the product if the rate at which additional hardware purchases becomes necessary decreases. The philosophy, IMHO, should be to solve the problems at hand with straight-forward OO solutions, and not to focus so much on being generic and supporting n * infinity solutions up-front. Using things like the Policy/Strategy pattern at well-selected locations will afford the opportunity for pluggability without compromising maintainability and performance.
Here are some dramatic results:
Direct:
public void init() { customer = new Customer(); }
public void run()
{
customer.work();
}
Interface (Polymorphism):
public void init() { customer = new Customer(); } public void run() { Person person = (Person) customer; person.work(); }
Reflection:
public void init() { customer = new Customer(); try { method = customer.getClass().getMethod("work", new Class[0]); } catch (Exception e) { } params = new Object[0]; } public void run() { try { method.invoke(customer, params); } catch (Exception e) { } }
With 1000000 of the above code, here were the results:
| JDK | DirectTest | InterfaceTest | ReflectionTest |
|---|---|---|---|
| Sun 1.4 | 52 ms | 54 ms | 543 ms |
| Sun 1.4 -server | 26 ms | 56 ms | 279 ms |
| Sun 1.3 | 124 ms | 128 ms | 2168 ms |
| Sun 1.3 -server | 41 ms | 58 ms | 2012 ms |
| IBM 1.3 | 75 ms | 78 ms | 2134 ms |
Reflection will significantly effect the performance of the system and should be avoided for any runtime operations. Where it should and could definitely be applied is with the dynamic generation and compilation of code, or generation of metadata. Otherwise, even at the recommendation of Sun, it should be avoided for runtime operations.
Best,
John C. Dale
Leo Simons wrote:
Jason Dillon wrote:
PS. Can someone write up something about the current state of the major component containers out there with a feature blurb... no soap boxes, just the facts jack.
What, no soap boxes? How on earth can anyone comply with that? ;) No wait,
you weren't asking me anyway, were you. Ah, e-mail already typed. Bummer.
= My Opinion =
You should *not* be evaluating component containers. You should save this discussion
for a later date and just code your way to 1.0. The basic design idea overview
below should show that most of the architectural concepts behind all these containers are
very similar. I've been experimenting (no, I will not plug it, you will just get confused) with
some reflection that will allow any component written for any of the below to run in any
of the other containers, and that is feasible, straightforward and performant.
So write your components to plug in whatever you have, do a nice IoC, SoC, SAI, AOP
setup, and you will be able to defer refactoring around an external container until much later.
But that's my opinion, and I have now said it three times, and your a responsible adult
(yep, its a guess, you could also be 11 years old :D). Switching soapbox mode off.
= Disclaimer =
Comparing component containers is comparing apples with pears. Avalon is by far the
biggest 'generic' project at the moment, for example, but recent developments utilize AOP
and interceptor architecture to support a much 'lighter' container-component api and
contract. Indeed, picocontainer was started by an avalon elder from the firm belief that
things should be simpler and smaller. So to actually evaluate all this stuff, you really should
spend a day or so delving into the websites and the code of all these projects, and backing
tech like nanning (nanning.codehaus.org) and aspectj (www.aspectj.org). I would start
by looking at pico/nano and xwork, then take a look at the tutorials for avalon-merlin.
The other projects have a smaller community atm, and I tend to value community size
and vibe.
Furthermore, I have strong opinions about stuff, and allegations to various projects, hence
this is not an objective overview, even though I tried to make it somewhat objective.
= Features/ design idea shorthands =
IoC = Inversion of Control, the idea that an application is controlled from the top down
SoC = Seperation of Coccerns, the idea that a class (aspect) should do one job and do it well
SAI = Seperation of API from Implementation, the idea that you define and code to work
interfaces
AOP = Aspect Oriented Programming, mostly lightweight nowadays where you add a chain
of interceptors around a method call that can handle orthogonal concerns
DecP = Declarative Programming, where you use a declarative-style language (usually xml) to
determine things like component wiring (ie your average tomcat config file, generalized)
EBP = Event Based Programming, basically making the inter-object method call asynchronous
and encapsulating such a call into some kind of event object that can be queued, modfied,
etc
= No particular order, incomplete list =
http://wiki.opensymphony.com/space/XWork - IoC, SoC, SAI, AOP, DecP, EBP. Nearing
1.0 release. Used in webwork2 (a competitor to struts). EBP very basic only. Lean and mean,
but not mature and some client-server web-layer specific assumptions. Don't like the XXXAware
interfaces. Very vibrant and active community and many famous peeps with J2EE experience
around at opensymphony.
http://www.picocontainer.org/ and http://www.nanocontainer.org/ -
IoC, SoC, SAI, AOP, DecP. 1.0 beta releases. Lean and mean and very extensible and
embeddable, developed by smart XP peeps, some stuff already in use in some apps, but
otherwise pretty much alpha. I love picocontainer and the way they're doing the project.
The dev community is intentionally kept small atm, but many peeps are watching this one.
http://plexus.codehaus.org/ - IoC, SoC, SAI, DecP. Container supporting
avalon-framework components. Used to be yet-another-novel-avalon-container, but I
think they're growing to be container-component-contract-agnostic. Corporate backed
development. Smart guys, not so much focussed on releases as on getting all the
functionality they need (which is a lot) in place. Very much a pragmatic project.
http://www.jcontainer.org/ - Not yet public container development
(dubbed 'loom' IIRC) by a smart ex-avaloner 'n others. Haven't seen any code yet
but my guess is it'll be good. The website says "move along" so you prolly should.
http://www.springframework.org/ - haven't looked at in too much depth. Seems similar to
nanocontainer and xwork. Think it has one active developer and a beta release. Some
smart points made, but too much xml for my taste. Hoping to see some of this rolled into
Xwork and/or pico.
http://avalon.apache.org/ - IoC, SoC, SAI, DecP, EBP (EBP for fortress only). By far
the oldest 'generic container' project. Big committer base, mature codebase, mature
ASF project (which can be a good thing and a bad thing ;) rather extensive
'avalon-framework' (comparatively heavy compared to more recent developments)
that defines the contracts between a component and a container. Has 3
container projects to consider: avalon-phoenix, a mature microkernel design,
avalon-fortress, similar in weight and featureset to something like nanocontainer with a
1.0 release (successor to avalon-ecm, the container used in (among other projects)
apache-cocoon), and avalon-merlin, a more recent development which we _seem_
to be converging on as the successor to all other previously produced containers. Merlin
is further described in the email by Stephen Mcconnell. Arguably the biggest,
most extensive and most dynamic IoC container implementation around (and hence
also the most complex). Re: my earlier blurb on 'geronimo and avalon' for more
yadayada.
http://jakarta.apache.org/commons/sandbox/hivemind - haven't looked at in much detail, but seems
very similar in scope and setup to avalon at first glance. Framework being refactored out
of hibernate, one developer, still in alpha with no releases I think. No offense to Howard
intended, but I think he's cut himself a rather big piece of the puzzle to recode from scratch
at once. But I am an uninformed whiner, so I'm not going to comment further in the hope that
Howard will just eventually see the light and direct his energy towards collaboration with the
avalon peeps :P
I am spending too much time on writing messages to this mailing list (it is nearly 3am over here).
I promise this is the last message from me for two weeks :D
g'night,
- Leo
