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.
- Name Attribute Match - @Resource with a name attribute matching the resource name gets that resource injected
- Injected Name Match - variable name matching the resource name gets that resource injected
- 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.class) @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>