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Command pattern vs Session Facade  RSS feed

Kelly Vista
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I am debating using the Command pattern as my primary strategy for implementing my J2EE enterprise app business logic and would like some advice.

The general idea is to have only a few types of abstract commands (such as a NonTransactionalCommand, a TransactionalCommand -- I might have a slightly finer granularity than this, I don't know) and implement each use case as a command instance. For example, I might have a command called GetProductListCommand which is a NonTransactionalCommand and returns the list of products available (i.e., has a getProducts() method) when execute()'d.

The result of my design will be a very small set of stateless session beans with an execute() interface. No entity beans (will use Hibernate) and may very well eventually implement a Message bean interface with a similar executeAsynchronously() type method, if eventually necessary.

I guess the popular alternative (or, more correctly, the norm) is to implement session facades for this.

However, I am attracted to the Command pattern because of its simplicity, it's rapid application development angle, its disconnected-ness from EJB (e.g., a modification to a command does not mean touching any EJB at all, just the command class), and the ability for implementing cross-cutting features (such as transactions or security, although I also plan to use an AOP solution at the POJO level). At the same time, it works as a delegate of an EJB, so it's accessible for all kinds of network clients.

I am also familiar with it's drawbacks (e.g., maintainability for large numbers of commands, per the literature, such as the Marinescu 2002 EJB Patterns book).

So, very few types of stateless session beans (though there may be many instances) -- mainly there for remote client acceessibility and the ability to leverage application-level transactions if needed.

Nevertheless, I have never tried the command pattern approach and was curious if others had feedback or case studies.

Best regards --
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