DI in EJB / MDB Application

Question

I am currently developing a small EJB application running on IBM Websphere Application Server 7 (Java EE 5). The application basically consists of one MDB, which listens for incoming MQ messages, which are converted and stored in the database. I currently use a lot of Singleton / Factories for sharing configurations, comparisons, data searches, etc. But this actually leads to very complex code testing. The solution can use a (simple) DI structure, such as guice / spring, to input different instances. The question is: where to place the initialization / configuration code? Where is the main entry point of the application? How can I inject instances in MDB?

Answer 1

Using Spring, you can do this through EJB3 interceptors, see http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/ejb.html#ejb-implementation-ejb3

Useful warning information is provided in javadoc, make sure you read it: http://static.springsource.org/spring/docs/3.0.x/api/org/springframework/ejb/interceptor/SpringBeanAutowiringInterceptor.html

Answer 2

it might be worth taking a look at the rollback from using Guice and trying to work with the injection mechanisms that are already available with Java EE 5.

Regarding finding a suitable “starting point”, unfortunately, the EJB specification does not define the way you can run a bean at startup. However, the EE specification web profile has one thing: you can add a WAR to your application and install the servlet listener component:

http://java.sun.com/javaee/5/docs/api/javax/servlet/ServletContextListener.html

You can set this to run when the application is loaded and launched by the container (WebSphere). However, pay attention to problems with class loaders.