How to combine Session Facade and Transfer object?

Question

Hello All!
I'm working on an enterprise application. Presentation layer is a stand alone client, business logic is build on the Glassfish v2.1 and MySQL is used as a database. The client is connection to the GlassFishj server remotely using EJBs.
I have problems with business logic architecture.
Here is the brief description of backend application architecture design:
1. Session Facade pattern is used to simplify the client and application server interface and to provide application layers between backend (http://java.sun.com/blueprints/corej2eepatterns/Patterns/SessionFacade.html).
2.Transfer Object pattern to define update transfer objects strategy in order to decrease network overhead during client and application server interactions and to provide version control for objects. Transfer objects are designed as simple java business serializable objects. (http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html)
3. Originally the backend application consisted of three modules: users, storage and orders, but at the end I have decided to divide my application into the following parts - assortments, map, menu, orders, transactions, users.
4. All MySQL database transactions are via JDBC using procedures. No use of entity beans.
Questions:
1. I have some doubts about using Session Facade and Transfer object patterns at the same time. At first I'd mike to cite the definitions of the patters from the SUN official web site.
* Use a session bean as a facade to encapsulate the complexity of interactions between the business objects participating in a workflow. The Session Facade manages the business objects, and provides a uniform coarse-grained service access layer to clients.
* Use a Transfer Object to encapsulate the business data. A single method call is used to send and retrieve the Transfer Object. When the client requests the enterprise bean for the business data, the enterprise bean can construct the Transfer Object, populate it with its attribute values, and pass it by value to the client.
* So, if I use Transfer Object along with Session Facade, it makes some difficulties with object version control, because I 2 or
3 transfer objects controls with the 1 bean class. The best option for Transfer object Pattern is that each transfer object should have its own bean class to provide ability of object's version control. In the case it can bring the network overhead because of frequent remote calls caused by the large number of the bean classes.
* So, should I use the both patterns? If yes, how to manage the interaction the patterns. If no, which one to use.
2. E.g. I have a huge list of the Order objects and each Order object consists of other complicated objects. So, would I have trouble to transfer that list over network? If yes, how to manage it.
Thank you!
Astghik

Answer 1

Astghik wrote:
Hello All!
I'm working on an enterprise application. Presentation layer is a stand alone client, business logic is build on the Glassfish v2.1 and MySQL is used as a database. The client is connection to the GlassFishj server remotely using EJBs.
I have problems with business logic architecture.
Here is the brief description of backend application architecture design:
1. Session Facade pattern is used to simplify the client and application server interface and to provide application layers between backend (http://java.sun.com/blueprints/corej2eepatterns/Patterns/SessionFacade.html).
I would simply recommend establishing a service tier. Your services should be stateless. You can go the extra mile and have a session facade, but in the majority of cases, coding to an interface for your service accomplishes the same goals.
2.Transfer Object pattern to define update transfer objects strategy in order to decrease network overhead during client and application server interactions and to provide version control for objects. Transfer objects are designed as simple java business serializable objects. (http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html)
The idea of the transfer object is very similar to the Command pattern. I think if you investigate that pattern, it will be more obvious. The transfer object reduces network latency by consolidating all the parameters into an object, ideally, this also consolidates multiple method calls. If you combine a transfer object (or command object) with a service tier, you get the best of both worlds. The service can delegate calls to helper objects (or other services or components) using the data in the transfer / command object.
3. Originally the backend application consisted of three modules: users, storage and orders, but at the end I have decided to divide my application into the following parts - assortments, map, menu, orders, transactions, users.
The is your domain. It will vary from application to application. The principles above are more general (e.g., patterns and architectural tiers) and should apply to most domains. However, your actual use case may require something different.
4. All MySQL database transactions are via JDBC using procedures. No use of entity beans.
Consider using something like iBatis or Spring's JDBC templating to make your life easier with JDBC.
Questions:
1. I have some doubts about using Session Facade and Transfer object patterns at the same time. At first I'd mike to cite the definitions of the patters from the SUN official web site.
* Use a session bean as a facade to encapsulate the complexity of interactions between the business objects participating in a workflow. The Session Facade manages the business objects, and provides a uniform coarse-grained service access layer to clients.
* Use a Transfer Object to encapsulate the business data. A single method call is used to send and retrieve the Transfer Object. When the client requests the enterprise bean for the business data, the enterprise bean can construct the Transfer Object, populate it with its attribute values, and pass it by value to the client.
* So, if I use Transfer Object along with Session Facade, it makes some difficulties with object version control, because I 2 or
3 transfer objects controls with the 1 bean class. The best option for Transfer object Pattern is that each transfer object should have its own bean class to provide ability of object's version control. In the case it can bring the network overhead because of frequent remote calls caused by the large number of the bean classes.
* So, should I use the both patterns? If yes, how to manage the interaction the patterns. If no, which one to use.
Versioning is a separate issue. Generally, the more coarsely grained your transfer / command object is, the more changes are likely to impact dependent objects.
Your command or transfer object does not have to be a vanilla JavaBean, where you are basically creating a bean that has data from other objects. You can simply use your command / transfer object to encapsulate already existing domain objects. I see no need to map to a JavaBean with what you have described.
Generally, a method signature should be understandable. This means that many times it is better to pass the method, say, two coarsely grained objects than a signature with a dozen primitives. There are no hard and fast rules here. If you find a method signature getting large, consider a transfer / command object. If you want one service to delegate calls to a number of other services, you can also create a transfer / command object to furnish the controlling service with the data it needs to invoke the dependent services.
2. E.g. I have a huge list of the Order objects and each Order object consists of other complicated objects. So, would I have trouble to transfer that list over network? If yes, how to manage it.
This is a large, open-ended question. If you are going to display it to a user on a screen, I do not see how you avoid a network transfer with the data. The general answer is to not pass the data itself but rather a token (such as a primary key, or a primary key and a start and stop range such as you see on a Google search result). You do want to limit the data over the network, but this comes at a cost. Usually, the database will receive additional load. Once that becomes unacceptable, you might start putting things into session. Then you worry about memory concerns, etc. There is no silver bullet to the problem. It depends on what issues you are trying to address and what trade-offs are acceptable in your environment.
Thank you!
AstghikBest of luck.
- Saish