In order for a BMP entity bean to work, it must have access to the database or resource to which it will persist itself. To get access to the database, the bean usually obtains a resource factory from the JNDI ENC. The JNDI ENC is covered in detail in Chapter 11, but an overview here will be helpful since this is one of the first times it is actually used in this book. The first step in accessing the database is to request a connection from a DataSource , which we obtain from the JNDI environment naming context:

private Connection getConnection( ) throws SQLException {
    try {
        Context jndiCntx = new InitialContext( );
        DataSource ds = (DataSource)jndiCntx.lookup("java:comp/env/jdbc/titanDB");
        return ds.getConnection( );
    }
    catch (NamingException ne) {
        throw new EJBException(ne);
    }
}

In EJB, every enterprise bean has access to its JNDI environment naming context (ENC), which is part of the bean-container contract. The bean’s deployment descriptor maps resources such as the JDBC DataSource, JavaMail, J2EE Connector, and Java Message Service to a context (name) in the ENC. This provides a portable model for accessing these types of resources. Here’s the relevant portion of the deployment descriptor that describes the JDBC resource:

<enterprise-beans>
    <entity>
        <ejb-name>ShipEJB</ejb-name>
        ...
        <resource-ref>
            <description>DataSource for the Titan database</description>
            <res-ref-name>jdbc/titanDB</res-ref-name>
            <res-type>javax.sql.DataSource</res-type>
            <res-auth>Container</res-auth>
        </resource-ref>
        ...
    </entity>
    ...
</enterprise-beans>

The <resource-ref> tag is used for any resource (e.g., JDBC, JMS, Connector, JavaMail) that is accessed from the ENC. It describes the JNDI name of the resource (<res-ref-name>), the factory type (<res-type>), and whether authentication is performed explicitly by the bean or automatically by the container (<res-auth>). In this example, we are declaring that the JNDI name jdbc/titanDB refers to a javax.sql.DataSource resource manager and that authentication to the database is handled automatically by the container. The JNDI name specified in the <res-ref-name> tag is always relative to the standard JNDI ENC context name, java:comp/env.

When the bean is deployed, the deployer maps the information in the <resource-ref> tag to a live database. This is done in a vendor-specific manner, but the end result is the same. When a database connection is requested using the JNDI name java:comp/jdbc/titanDB, a DataSource for the Titan database is returned. Consult your vendor’s documentation for details on how to map the DataSource to the database at deployment time.

The getConnection( ) method provides us with a simple and consistent mechanism for obtaining a database connection for our ShipBean class. Now that we have a mechanism for obtaining a database connection, we can use it to insert, update, delete, and find Ship EJBs in the database.