Configuring DataSources

Configuring DataSources in openejb.xml

The <Resource> element is used to configure a javax.sql.DataSource. It is also used to configure other resources like Timers, Topics, Queues. We will see some examples of using <Resource> to configure a DataSource.

The <Resource> element is designed after @Resource annotation and has similar attributes.

For example, this annotation in your bean:

@Resource(name = "myDerbyDatasource", type = javax.sql.DataSource.class)

Would map to a Resource declared in your openejb.xml as follows:

<Resource id="myDerbyDatasource" type="javax.sql.DataSource">
 . . . .
<Resource>

Note that in the xml element, the type value of javax.sql.DataSource can abbreviated to just DataSource as follows:

<Resource id="myDerbyDatasource" type="DataSource">
 . . . .
<Resource>

See Containers and Resources for a complete list of supported DataSource properties. See DataSource Password Encryption for information on specifying non-plain-text database passwords in your openejb.xml file. See Common DataSource Configurations for a list of the commonly used databases and their driver configurations.

JNDI names for configured DataSources

Example 1

<Resource id="Default JDBC Database" type="DataSource">
   . . . . .
</Resource>

The global jndi name would be java:openejb/Resource/Default JDBC Database

Example 2

<Resource id="Derby Database"  type="DataSource">
  . . . . .
</Resource>

The global jndi name would be java:openejb/Resource/Derby Database

Obtaining a DataSource

DataSource references in your ejb should get automatically mapped to the Resource you declare. The shortest and easiest rule is that if your reference name matches a Resource in your openejb.xml, that's the one you get.  Essentially, the rules for mapping are as follows.

1. Name Attribute Match - @Resource with a name attribute matching the resource name gets that resource injected
2. Injected Name Match - variable name matching the resource name gets that resource injected
3. No Match - nothing matches a resource name, so the first resource available gets injected

There are various ways one could obtain a DataSource now. Lets take an example of Derby.

With a Resource declaration in your openejb.xml like this:

<Resource id="myDerbyDatabase"  type="DataSource">
  . . . . .
</Resource>

There are several possible ways to refer to it, as follows.

BY matching variable name to resource name

@Stateless
public class FooBean {
    @Resource DataSource myDerbyDatabase;
}

OR BY matching name

@Stateless
public class FooBean {
    @Resource(name="myDerbyDatabase")
    DataSource dataSource;
}

OR BY JNDI lookup

@Resource(name="myDerbyDatabase", type="javax.sql.DataSource")
@Stateless
public class FooBean {

    public void setSessionContext(SessionContext sessionContext) {
        DataSource dataSource = (DataSource) sessionContext.lookup("myDerbyDatabase");
    }

    public void someOtherMethod() throws Exception {
        InitialContext initialContext = new InitialContext();
        DataSource dataSource = (DataSource) initialContext.lookup("java:comp/env/myDerbyDatabase");
    }
}

OR

<resource-ref>
   <res-ref-name>myDerbyDatabase</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
 </resource-ref>

OR

<resource-ref>
   <res-ref-name>jdbc/myDerbyDatabase</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
 </resource-ref>

OR

<resource-ref>
   <res-ref-name>someOtherName</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <mapped-name>myDerbyDatabase</mapped-name>
 </resource-ref>