在EJB项目中使用Jboss动态加载DataSource

Question

lets consider I have one main database with one table.

I created a datasource xml file inside the deploy directory from jboss and put inside the ejb project into the persistance.xml that datasource.

Inside my ejb project I am using the @PersistenceContext and load this one table with that entity manager. Inside the table are the some datasource names (the datasource names are jndi datasource names?) I also created in the deploy directory before. This bean who loaded the other datasource names now call other ejbs and passes them one of the datasource names from the table.

This other ejb should now connect to that database with the given datasource name instead of the inside the persistance.xml.

In other words: I want to load in one ejb the datasource names. Then I want to call other ejbs and each ejb should connect to a different datasource.

Thanks a lot, Hauke

Answer 1

I'm not quite sure what you're after here, so a word of caution is sounds like you're trying to do something a wee bit insane (the JPA doesn't like dynamics at runtime).

However, there are a few options: what I'm hearing is that you want to change the connection to the database. First, your persistence XML is only a starting point, you don't have to include a datasource. This isn't best practice as the idea of the DataSource and datasourse-ds.xml is to make sure you can configure the application without recompiling the code (and multiple deployments etc...). If you take over the job of managing the connection you can use your entity manager.

I just want to clarify this is probably a bad idea (you're talking about an ORM framework --JPA Hibernate in this case) but instead of using @PersistenceContext you can provide your own entity manager. I highly recommend looking into using EclipseLink as a workaround for this. It is not as embedded with JBoss and you'll be able (once it is running) to configure it from the ground up.

http://wiki.eclipse.org/EclipseLink

Once you have it running you can actively create and destroy the entity managers, or have numerous entity manager that you create from the properties of a connection.

The long and short here: I think you're going down a very bad path and you probably want to rethink the design. The JPA might be the wrong tool, and as much as I hate to say it, you're probably better off with javax.sql than you are with a JPA datasource if you're constantly changing connections.

Anyhow, using Eclipselink2.X you could do something like the following ->

HashMap<String, Object> connectionA new = HashMap<String, Object>();
propsA.put("javax.persistence.jdbc.driver", "driverClass");
propsA.put("javax.persistence.jdbc.url", "connectionString");
. . .
etc...
EntityManager entityManager = Persistence.createEntityManagerFactory("myUnit").
createEntityManager(propsA);

At which point you can create a new set of properties (With a new connection backing it) for each needed manager.

A nightmare? Yes. Container Managed? No--you'll be in-charge of handling transactions, but should it work? Absolutely.