Question

I am about to make a connection to my database and I am using EJB and JPA. I have recently started doing these technologies so I have some problems understand it all at this point:)
I know that the persistence.xml is needed in order to use JPA. It is the file where I configure how to connect to the database, that I know. However it seems like there are multiple ways of doing it.

What would be the difference (or when should I even use the one alternative over the other?) of defining properties such as username, database, password etc. in the persistence.xml file and in Glassfish? Advantages/disadvantages if any.

Underneath on the image I posted I have JDBC Resources and JDBC Connection Pools. I am a litte confused about the terminology of the two. Why don’t we add properties such as username, database, password and so on in the JDBC Resources? Could someone explain the difference between them and what they mean?

JDBC Resources

A JDBC resource (data source) provides applications with a means of
connecting to a database. Typically, the administrator creates a JDBC
resource for each database accessed by the applications deployed in a
domain. (However, more than one JDBC resource can be created for a
database.)
http://download.oracle.com/docs/cd/E19316-01/820-4335/ablih/index.html

I think it strange that we add such properties on the pool but not in the resource, but I probably misunderstand the concepts.

Answer 1

In the “JDBC connection pools” you can create container managed JDBC data sources (with connection pooling capabilities). The data source needs to know about at least the JDBC driver, the JDBC URL, username and password.

In the “JDBC resources” you can bind those container managed JDBC data sources to one or more JNDI names so that they are by JNDI available to the deployed web application.

In the persistence.xml you can specify whether to use a local data source or to use a container managed data source. If you want to use a container managed data source, then you should specify its JNDI name. Using a container managed data source has the advantage that you can share a single data source among multiple web applications. In case of JPA, it has also the advantage that you can make use of JTA (container managed transactions) so that you don’t need to call transaction.begin(), commit(), rollback() etc in every method.