Friday, June 24, 2011

JPA: Don't use JPA's RESOURCE_LOCAL on the server


The JPA 1.0 / 2.0 specifications are clear about the JTA or / RESOURCE_LOCAL usage on application servers:

"The transaction-type attribute is used to specify whether the entity managers provided by the entity manager factory for the persistence unit must be JTA entity managers or resource-local entity managers. The value of this element is JTA or RESOURCE_LOCAL. 

A transaction-type of JTA assumes that a JTA data source will be provided—either as specified by the jta-data-source element or provided by the container. In general, in Java EE environments, a transaction-type of RESOURCE_LOCAL assumes that a non-JTA datasource will be provided.

In a Java EE environment, if this element is not specified, the default is JTA. In a Java SE environment, if this element is not specified, the default is RESOURCE_LOCAL."

See section 8.2.1.2, Page 312 from JSR317


If you deploy the following persistence.xml:

<persistence>
  <persistence-unit name="integration" transaction-type="RESOURCE_LOCAL">
    <class>...AnEntity</class>
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby:memory:testDB;create=true"/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
      <property name="eclipselink.ddl-generation" value="create-tables"/>
    </properties>
  </persistence-unit>
</persistence>

into a Java EE application server, you will also have to manage both: the EntityManager and it's JTA-transaction by yourself. This will end up with lots of plumbing. Instead of RESOURCE_LOCAL, you should use the JTA setting in production. With the JTA setting you don't have to specify the JDBC-connection and use a pre-configured JTA data source instead: 


<persistence>
  <persistence-unit name="prod" transaction-type="JTA">
    <jta-data-source>jdbc/sample</jta-data-source>
    <properties>
      <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
    </properties>
  </persistence-unit>
</persistence>