[Engine-devel] Simplifying our POJOs

[Mike Kolesnik]

----- Original Message -----
> On 31/01/12 12:39, Livnat Peer wrote:
> > On 31/01/12 12:02, Mike Kolesnik wrote:
> >> Hi,
> >>
> >> Today many POJO
> >> <http://en.wikipedia.org/wiki/Plain_Old_Java_Object>s
> >> are used throughout the system to convey data:
> >>
> >>   *   Parameters - To send data to commands.
> >>   *   Business Entities - To transfer data in the parameters &
> >>   to/from
> >>     the DB.
> >>
> >> These POJOs are (usually) very verbose and full of boilerplate
> >> code
> >> <http://en.wikipedia.org/wiki/Boilerplate_code>.
> >>
> >> This, in turn, reduces their readability and maintainability for a
> >> couple of reasons (that I can think of):
> >>
> >>   * It's hard to know what does what:
> >>       o Who participates in equals/hashCode?
> >>       o What fields are printed in toString?
> >>   * Consistency is problematic:
> >>       o A field may be part of equals but not hashCode, or vice
> >>       versa.
> >>       o This breaks the Object.hashCode()
> >>         <http://docs.oracle.com/javase/6/docs/api/java/lang/Object.html#hashCode%28%29>
> >>         contract!
> >>   * Adding/Removing fields take more time since you need to
> >>   synchronize
> >>     the change to all boilerplate methods.
> >>       o Again, we're facing the consistency problem.
> >>   * These simple classes tend to be very long and not very
> >>   readable.
> >>   * Boilerplate code makes it harder to find out which methods
> >>   *don't*
> >>     behave the default way.
> >>   * Javadoc, if existent, is usually meaningless (but you might
> >>   see some
> >>     banal documentation that doesn't add any real value).
> >>   * Our existing classes are not up to standard!
> >>
> >>
> >> So what can be done to remedy the situation?
> >>
> >> We could, of course, try to simplify the classes as much as we can
> >> and
> >> maybe address some of the issues.
> >> This won't alleviate the boilerplate code problem altogether,
> >> though.
> >>
> >> We could write annotations to do some of the things for us
> >> automatically.
> >> The easiest approach would be runtime-based, and would hinder
> >> performance.
> >> This also means we need to maintain this "infrastructure" and all
> >> the
> >> implications of such a decision.
> >>
> >>
> >> Luckily, there is a much easier solution: Someone else already did
> >> it!
> >>
> >> Check out Project Lombok: http://projectlombok.org

If you're interested in just the effect and don't/can't watch the 3min demo on the site, I attached examples of a class before & after.

> >> What Lombok gives us, among some other things, is a way to greatly
> >> simplify our POJOs by using annotations to get the boilerplate
> >> code
> >> automatically generated.
> >> This means we get the benefit of annotations which would simplify
> >> the
> >> code a whole lot, while not imposing a performance cost (since the
> >> boilerplate code is generated during compilation).
> >> However, it's also possible to create the methods yourself if you
> >> want
> >> them to behave differently.
> >> Outside the POJO itself, you would see it as you would always see
> >> it.
> >>
> >> So what are the downsides to this approach?
> >>
> >>   * First of all, Lombok provides also some other capabilities
> >>   which I'm
> >>     not sure are required/wanted at this time.
> >>       o That's why I propose we use it for commons project, and
> >>       make use
> >>         of it's POJO-related annotations ONLY.
> >>   * There might be a problem debugging the code since it's
> >>   auto-generated.
> >>       o I think this is rather negligible, since usually you don't
> >>       debug
> >>         POJOs anyway.
> >>   * There might be a problem if the auto-generated code throws an
> >>   Exception.
> >>       o As before, I'm rather sure this is an edge-case which we
> >>       usually
> >>         won't hit (if at all).
> >>
> >>
> >> Even given these possible downsides, I think that we would benefit
> >> greatly if we would introduce this library.
> >>
> >> If you have any questions, you're welcome to study out the project
> >> site
> >> which has very thorough documentation: http://projectlombok.org
> >>
> >> Your thoughts on the matter?
> >>
> > 
> > - I think an example of before/after pojo would help demonstrating
> > how
> > good the framework is.
> > 
> > - Would it work when adding JPA annotations?
> > 
> >> Regards,
> >> Mike
> >>
> 
> Watching the demo it looks like we'll get less code, which in many
> cases is a good thing.
> What I'm concerned about is traceability; or- how can we track issues
> coming from the field
> when function calls and line numbers in the stack trace will not
> match the code we know.

As I said these are edge cases which although are important, I'm not sure if we will ever hit them.
Also bear in mind that you can still write your own code in the POJO, which will take precedence over the auto generated code, and I believe that for that code the lin numbers will be in-sync.

> 
> --
> 
> /d
> 
> "Willyoupleasehelpmefixmykeyboard?Thespacebarisbroken!"
> 
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