Java Magazine - May/June 2012

//enterprise java /

Convention over Configuration in Java EE 6

COMMUNITY

ADAM BIEN

Learn to specify the unconventional through Convention over Configuration.

JAVA IN ACTION

Convention over Configuration in Java EE 6 requires you to specify only the unconventional. Obvious choices do not have to be configured. However, some of the environmental or deployment-dependent choices simply cannot be derived from the convention and have to be configured. This article focuses on project-specific or product-specific configuration of Java EE 6 applications that require explicit configuration.

A Stage can be represented as an enum and injected to all interested resources:

public enum Stage { Development, Unit Test, System Test, Production }

PHOTOGRAPH BY THOMAS EINBERGER/ GETTY IMAGES

Staging

Information about the current stage (such as test, integration, or production) is particularly interesting for applications with high amounts of legacy code. Legacy connectors often are not fully Java EE–compliant and cannot use Java EE resource management. Instead of relying on the application server’s configuration capabilities, you have to mock out external resources in the prepro-duction stages.

The current stage can be explicitly configured as a system property, configuration file, database, or any resource you prefer. JavaServer Faces 2 (JSF 2) supports a configurable staging environment with the ProjectStage class, so we can expose the existing information with a managed bean (see Listing 1).

The ProjectStage class originates from the JSF 2 API and belongs to the UI layer. To decouple the business logic implementation from the UI, the FacesContextExposer managed bean (Listing 1) converts the ProjectStage into a neutral Stage enum. The method FacesContextExposer#stage()

“produces” the Stage and makes it available for injection. The staging value can be configured in the JNDI tree with the key java:comp/ env/jsf/ProjectStage or with the context-param tag in the web.xml deployment descrip-tor (see Listing 2). The JNDI key takes precedence—it overwrites the staging value configured in web.xml.

With the built-in annotation @Produces exposed, the Stage enum is directly injected as a Stage projectStage parameter of the ConnectorManager#connect method (see Listing 3).

Inside the connect method, the Stage enum is used to decide which EISConnector implementation to create. Only in the case of Stage.Production is the LegacyConnector created. For all other stages, EISMock is instantiated and returned. To distinguish a staged injection from the “usual” injection, the connect method is annotated with the