I've been holding off on this entry for some time. I wanted to wait until I left the place where I was using it so that I could feel able to be completely honest.
I'll be giving an user's eye view of it both from the perspectives of an architect and a developer, I'll talk about designing using it and developing with the artifacts. I've been using OptimalJ 3.2 which is a relatively old version, newer versions will have addressed some of the problems that I'll be raising. I'll mention any fixes that I am aware of.
Model Driven Architecture is yet another attempt to increase the application complexity while reducing development difficulty by drawing picures (usually UML) to define the components and code generation to produce them.
OJ contains a set of UML modelling tools, which are separate and distinct from the MDA tools. It did not seem to be possible to move the analysis and design done using OJ's own UML tools directly into the MDA tools. On the project that I was working on we used Rational Rose to do the analysis and design, before using OJ's MDA tools. The inbuilt UML tools were inferior to those in Rose.
Using OJ to produce the MDA models is little different from using a class modeller in an UML tool, defining classes, attributes and methods. Unfortunately aside from the class modelling most of the rest of the process is about walking through wizards or setting properties. A lot more thought could have gone into using more UML diagram types. For example when one wants to define dependencies between services, one has to add to the 'UsedComponent' property values. These kind of dependencies could be easily defined using collaboration or sequence diagrams.
The three major 'models' that OJ works with are the Domain Model (used to define the domain objects and services), Application Model (fleshing out the domain model and getting quite platform specific) and lastly the code model which is the generated code.
The following layers are defined by OJ by default in the Application Model:
- DBMS - The physical data model.
- Common - cross layer objects such as DTOs (in OJ speak UpdateObjects and DataObjects), OJ enumerations and structs.
- BusinessLogic - if I need to explain this one to you, perhaps you shouldn't be reading this... Well maybe I should explain one thing; BusinessLogic lumps Entity and Session Beans together and does not attempt to guide one down more structured approaches such as using the Session Facade pattern.
- BusinessFacade - a curious set of auto-generated facades that will try to use UserTransactions if you don't watch them very carefully. Mainly useful.
- Presentation - auto-generated struts forms and actions that are only really useful for data entry and prodding the services. In more recent versions of OJ a workflow designer has been added which will hopefully make this a lot more useful.
Out of the box one can only really architect J2EE/EJB applications, persistence only uses entity beans.
In practical use, OJ gets increasingly sluggish as the application increases in size. For what I would call a medium-small application we needed to wait anything up to a minute while OJ digested simple property changes; essential tools that check and update models that needs to be run frequently needed 10 minutes or more. It is also incredibly memory hungry, architects' machines were running with 2 gigabytes of RAM.
These problems can be managed by splitting your application into independent subsystems.
The code generation produces code that is split up into free and guarded blocks. Developers are expected to place business and application logic into the free blocks. I personally believe that weaving hand-cranked and generated code together in this way is a bad idea:
- It makes re-designing and re-factoring unnecessarily difficult as OJ is not properly joined up. If you change a class name or package, the developer code gets put into a 'recycle bin' and needs to be retrieved.
- The quality of code generated by the default patterns is more than a little suspect and makes it very difficult to get useful data out of reporting tools such as findbugs and checkstyle.
- It means that the model is not the thing. Not only do you have to check the model into your repository, you have to check in large swathes of generated code.
The code produced by the default patterns does not inspire confidence in the Java abilities of the people producing the application. For example a form of dirty marker pattern in provided to support the 'UpdateObject's (DTOs) produced in the common layer. Unfortunately it is one of the worst implementations that I have ever come across. The authors seem to have so little understanding of encapsulation that they require a developer to actually call a method to set a changed flag for each field manipulated. When one looks at an UpdateObject's interface, one sees nearly the entire workings of the OJ dirty marker pattern marked public for all to see and it is not a pretty sight. I was so outraged that I was very tempted to go and find the authors and slap them till they promised never to produce something like that ever again.
The version that I was using had one other significant failing, the model-merge functionality that allows multiple modellers to work simultaneously was broken and this introduced a major bottle nect.
Out of the box OJ falls into negative ROI. Any modern project using open source code generation can out-produce it.
Reading over what I have written it would seem that I hate it with a passion. That would be untrue. The potential is huge especially when one realises that one can rewrite the meta-models and patterns.
I would only recommend OJ to an organisation that had significant up-front time to invest:
- Take the time to really understand OJ's capabilities
- Improving the meta-model to provide a better breakdown of the business logic tier,
- Throw out many of the patterns and introduce new ones to use callback or dependency injection to move developer code out of the generated code.
- Produce patterns that make use of a wider range of technology.
- Write a decent dirty marker pattern.
- Wait for Compuware to make the generation steps full scriptable in ant.
- In monster computers for its architects.
Once all this had been done, then a positive ROI should materialise.
