Tuesday, September 1, 2009

SEAM - The Shopping Cart Web Application

Seam is ANOTHER web application framework. SIGH. Ok yes sigh another framework to learn but it is not entirely new, if you have been following along with the Shopping Cart tutorials where we used JSF, Facelets, Hibernate, JPA and RichFaces you will see that Seam is not something new just something extra.

This is not a tutorial in Seam more like a brief overview, introduction and comparison. Seam's documentation is pretty good to get started with. They also have sample applications so you can have a look to see how Seam is configured. I have also created a Seam web application based on the Shopping Cart application I did in previous posts. It is an Eclipse project. You will need to download the archived file and import it into your Eclipse workbench. I used JDK 1.6. The download is broken up into two parts simply because the file was too big to store on the server on its own:

  • ShoppingCartSeam.zip - This is the main archive that contains all 4 projects.
  • jboss-embedded-all.jar - A library used to run the embedded JBoss server when running our tests. Once you have imported the ShoppingCartSeam.zip archive into your Eclipse workbench please copy this file to the lib folder of the shopping-cart-test project.

Shopping Cart
I will highlight the major differences between the shopping cart application (that I will call Spring Application) we did in previous tutorials with this Seam shopping cart application.

1. Class diagrams
Below you will be able to compare the class diagram of the Spring application with the class diagram of the Seam application.

Spring class diagram

Seam class diagram

2. Spring vs EJB3
The design of our two applications stays pretty much the same, we still have our 3-tier architecture, i.e.
  • Presentation - GUI
  • Application - Business Logic
  • Data - Database

The difference being:
  • In the Spring application we have loosely coupled our application tier from our presentation tier by using Spring to manage and configure how we use and call our business layered objects. The view package contains all the logic for our GUI and is separated from our business logic. Also we use Spring to manage and configure our transactions.
  • In the Seam application we have tightly coupled our application tier to our presentation tier using Seam annotations and EJB3. There is some debate whether this is good or bad, at the end of the day they both have their advantages and disadvantages and it really depends on the type of project you are working on before deciding on which is better or worse. The Seam application uses an EJB3 session bean.

3. EAR vs WAR
The Spring application was packaged as a WAR as it didn’t have any EJB’s there was no need to create an EAR for it. There were two projects:
  • shopping-cart-web – web application
  • shopping-cart-core – project that contains all our business logic classes. It gets packaged as a JAR file and then added to our web application

Because it is packaged as a WAR we also didn’t need a full blown JEE server to deploy it to so Tomcat did the job quite nicely for us.

The Seam application is packaged as an EAR as it makes use of EJB3’s session beans. The project structure that was created for me when I used JBoss Tools to create a Seam project was the following:
  • shopping-cart – main web app
  • shopping-cart-ear – contains 3rd party libraries as well as datasource resource file used to connect to database
  • shopping-cart-ejb – EJB project that contains all our business logic classes (our entity beans and session beans)
  • shopping-cart-test – a standalone project that contains all our test classes

4. Entity classes
Both projects use the Java Persistence API (JPA) in the Entity classes (Basket, Item and BasketItem) to manage relational data and therefore the Entity classes are the same.

5. Faces Managed Beans
In our Spring application we are using the standard JSF library to manage our beans. We define our managed beans and set properties for it in the faces-config.xml file.

In the Seam application we define our managed beans in the beans class by using a Seam annotation (the annotation is called name and occurs just above the class declaration). Only navigational rules are defined in the faces-config file.

6. Web deployment descriptor
The Seam application has an additional filter and servlet defined in the web deployment descriptor, namely:

 <filter-name>Seam Filter</filter-name>
 <filter-name>Seam Filter</filter-name>
 <servlet-name>Seam Resource Servlet</servlet-name>
 <servlet-name>Faces Servlet</servlet-name>
 <servlet-name>Seam Resource Servlet</servlet-name>

In the Spring application I created .jspx files for our web pages. I would have preferred to use .xhtml but Eclipse didn’t recognize code completion for me and showed that there were warnings when in actual fact there weren’t. I am sure there is some tweak out there to get rid of the warnings and to include code completion but I couldn’t find it and the hassle was not worth the time spent on it. So instead I used .jspx files which worked nicely for me.

In the Seam application I installed the JBoss Tools plugin for Eclipse and .xhtml files seemed to work fine without any errors.

8. Session vs Conversation
Seam introduces two new contexts, conversation and business process. In the Spring application I define the ShoppingViewHelper class with Session scope in the faces-config.xml file.

I could have done the same with the Seam application (by adding another Seam annotation to my class called Scope and given it a value of Session) instead I opted for the better more manageable context provided by Seam called Conversation context.

9. JUnit vs TestNG
In the Spring application we used the JUnit test framework for all our unit tests.

TestNG is another test framework that works the same as JUnit. TestNG is the default test framework chosen by Seam. You are not restricted to TestNG and can can still use JUnit if you like. You can create unit tests just like we did in the Spring application. Seam allows you to create integration tests quite easily to test a complete process from request to response without too much of an overhead. In order to do this Seam uses an embedded JBoss server. The embedded JBoss server is a lightweight server that only starts up the necessary services required to test your application.

Seam application:

The sample application was a really basic one, there is a lot more to Seam than what I touched on here.
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