CDI gotcha

I learned this the hard way and wanted to make sure other people could benefit. While putting together a Java EE 6 application, I had put together a @SessionScoped bean that inherited from an abstract superclass.  Both the super- and subclass have injection points.  The subclass uses @Inject; the superclass only uses @PersistenceContext. Now, I had added the required META-INF/beans.xml file to the jar file housing the subclass, but never thought to add it to the superclass jar file, since of course when I wrote the superclass I wasn't thinking CDI at all (and actually as it happened when I wrote the abstract superclass it was in the Java EE 5 days), so why would I have packaged it into a bean archive? But it turns out--somewhat unintuitively--that if you inherit from a class that has an injection point in it--even if the injection point is defined in terms of Java EE and not CDI--and if that abstract class comes from a jar that is not a bean archive, then dependency injection by the CDI provider will not be applied to its injection point until you make sure that its jar file contains a META-INF/beans.xml file. A simpler way to put this is that for any given inheritance chain, all jars in the chain containing classes with injection points must be bean archives. (On a totally unrelated subject, the documentation links in this post are to the horrific new documentation URLs that Oracle has seen fit to imp...

Date: July, 23 2010
Url: http://www.java.net/blog/ljnelson/archive/2010/07/23/cdi-gotcha

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