I can't find any functioning way for Spring with Annotations to create and inject an EntityManager object for me, backed by JPA and Postgres.
Can anyone share the minimal set of @Bean methods in an @Configuration-annotated object to get JPA working against Postgres?
I've created a minimal test application in an ordinary Eclipse Java project to show my working so far. I think everything should be self explanatory (and the error is probably located) in App.java linked below.
In App I'm trying to create an AnnotationConfigApplicationContext and get it to use the annotated methods in App.Config as a factory for a DataSource and an EntityManagerFactoryInfo. Then I try to load an EntityManager bean from the ApplicationContext, thinking it has enough information to proceed.
Running my code triggers no errors until the terminal error "No unique bean of type [javax.persistence.EntityManager]" when I try to load the EntityManager bean
I'm sure I'm just doing the wrong thing, but I can't find a simple statement of the minimal chain of events/requirements to configure and inject an EntityManager into my App. Currently it seems to think there is no definition of an EntityManager despite the EntityManagerFactoryInfo object and DataSource object available.
I figure all I need to provide is a database, and the right incantation somewhere in annotations or maybe java BeanDefinition passing, after which everything will work like magic.
I've set up and tested the database, but the magic incantation is eluding me. My aim is to avoid mysterious unvalidated XML files so I'm focusing on Annotations, or maybe even direct Java calls if anyone knows how, to configure and trigger the DI.
After much trial and error, (and I really mean a lot), I've had to give up and throw myself on your mercy.
I'm trying to avoid loading in a million and one unnecessary things from a test application configured by Maven and reams of boilerplate XML to establish if Spring components can be used in a more comprehensible and selective way.
The core example code of the approach I'm using so far is available in the App file, and the libraries on the build path of the Eclipse project are shown in the listjars.txt file also linked below.
When I run this App as is, I get no errors until my explicit getBean(EntityManager.class) call fails with...
Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefini tionException: No unique bean of type [javax.persistence.EntityManager] is defined: expected single bean but found 0:
at org.springframework.beans.factory.support.DefaultL istableBeanFactory.getBean(DefaultListableBeanFact ory.java:269)
at org.springframework.context.support.AbstractApplic ationContext.getBean(AbstractApplicationContext.ja va:1083)
App.java is available at...
The libraries in my Build path are listed here...
...and the remainder of the source is available by browsing around the src directory in the github tree if that helps.
Constructors and other established java conventions normally steer you towards resolving dependencies, and prevent runtime failures.
I find that Spring's divergence from this approach makes it more or less impossible for me to identify the minimal functioning configuration for any object, and leaves failures silent until service objects are demanded.
For EntityManager and JPA there now seems to be a history of about a thousand different recommended ways to do it, all using arcane XML files and most of which are now deprecated, and there are many suggested alternatives even for the recommended routes.
How am I meant to approach this problem in general as I'm sure I'll run into it in other parts of Spring?