在容器外使用 EJB

Question

I am currently creating a J2EE application and there is a part of it that is running outside the container, using a ServletContextListener to launch it.

However I also need to access the database from this part.

I currently have an Entity and a Stateless Session bean to fetch use the EntityManager.

I tested multiple things ( EntityManagerFactory, Initial Context, EJBContainer ) but I didn't manage to make any of them work.

How do I need to do it?

Answer 1

You do not need EJB, actually you cannot create Ejbs outside the container. You need JPA, an OR-mapper and JDBC. These normally are correctly configured in your EJB-Container. Outside the container you have to do that yourself.

You have to define your dependencies right, so that the correct JDBC-Driver is available and the OR-Mapper (probably eclipselink or hibernate?) After that, you need define a presistence.xml to define the Entities to be used and to define how the DBMS is accessed via JDBC.

If that all is correctly configured EntityManagerFactory is the correct way to create an EntityManger for the persistence-unit defined in persistence.xml.

There are many examples available on the net. eg:

• https://examples.javacodegeeks.com/enterprise-java/jpa/java-persistence-xml-example/ should work, if you are using eclipselink.
• https://docs.jboss.org/hibernate/orm/3.6/quickstart/en-US/html/hibernate-gsg-tutorial-jpa.html in case of Hibernate.