On silly Java mistakes

So you’re getting started with your Java EE web project and you’re using JPA, annotations, dependency injection, all that good stuff. Except when you launch your awesome web app, your Glassfish 3 server spits out something like this:

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: javax.ejb.CreateException: Could not create stateless EJB

root cause

javax.ejb.CreateException: Could not create stateless EJB

root cause

java.lang.IllegalStateException: Exception attempting to inject Env-Prop: org.example.EjbClass/emf@Field-Injectable Resource. Class name = org.example.EjbClass Field name=emf@java.lang.String@@@ into class org.example.EjbClass: Can not set javax.persistence.EntityManagerFactory field org.example.EjbClass.emf to com.sun.enterprise.container.common.impl.EntityManagerWrapper

root cause

com.sun.enterprise.container.common.spi.util.InjectionException: Exception attempting to inject Env-Prop: org.example.EjbClass/emf@Field-Injectable Resource. Class name = org.example.EjbClass Field name=emf@java.lang.String@@@ into class org.example.EjbClass: Can not set javax.persistence.EntityManagerFactory field org.example.EjbClass.emf to com.sun.enterprise.container.common.impl.EntityManagerWrapper

root cause

java.lang.IllegalArgumentException: Can not set javax.persistence.EntityManagerFactory field org.example.EjbClass.emf to com.sun.enterprise.container.common.impl.EntityManagerWrapper

If you’re reading the error message carefully, like my friend didn’t, you’ll notice that it’s complaining about trying to set an EntityManager instance on an EntityManagerFactory field.

Why, oh why, would it do this?

Because you’re using the @PersistenceContext annotation on the field, instead of @PersistenceUnit. Ouch.

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