[Engine-devel] Simplifying our POJOs

[Doron Fediuck]

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
>> 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.

-- 

/d

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