Question

I am trying to understand the following things:

When I make an EJB project and deploys it to Glassfish do I set up JDBC resources/connection pools at the administrator center of Glassfish or do I add all the different properites for username, password etc in the persistence.xml? I don’t understand one bit of that.

I do not understand why we have both JDBC resource and JDBC Connection pool either. What is it and what is the difference between them? Could somebody explain me these things or/and provide some good link about the persistence.xml file and the part around it?

Answer 1

It’s better to define a JDBC resource rather than putting the information in the persistence.xml. In this way you are going to take advantage of connection pooling. You are going to define the JNDI name you provided for the JDBC resource in the persistence.xml.

What is it and what is the difference between them

Below I pasted some parts of the Glassfish 3.x help. Check it out. It’s really helpful

JDBC connection pool

A JDBC connection pool contains a group of JDBC connections that are created when the connection pool is registered

JDBC resource

A Java DataBase Connectivity (JDBC) resource (data source) provides applications with the 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.

Applications get a database connection from a connection pool by looking up a data source on the Java Naming and Directory Interface (JNDI) API tree and then requesting a connection. The connection pool associated with the data source provides the connection to the application.

Think of the data source(JDBC) resource as a factory for a facade of some type of data service(Connection Pool). In this case it implicitly gets a connection from the pool and provides it to your application.

An example persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="WebApplication2PU" transaction-type="JTA">
    <jta-data-source>jdbc/sample</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties/>
  </persistence-unit>
</persistence>

This line is the JNDI name I gave to my JDBC resourse:

 <jta-data-source>jdbc/sample</jta-data-source>

You dont need to define anything related to the database connection in your persistence.xml this way…just the JNDI name of the resource