Java Persistent Objects

Any JDO-enabled application will require at least one PersistenceManagerFactory (PMF). Typically applications create one per datastore being utilised. PMFs can be created in many ways, and a way that is new in JDO2.1 is to have a "named" PMF. This utilises a configuration file that defines the named PMFs. This configuration file is called jdoconfig.xml.

jdoconfig.xml

The file jdoconfig.xml defines the named PMFs and is stored at META-INF/ in the application jar/CLASSPATH. Let's see an example of a jdoconfig.xml

<?xml version="1.0" encoding="utf-8"?>
<jdoconfig xmlns="http://java.sun.com/xml/ns/jdo/jdoconfig"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="http://java.sun.com/xml/ns/jdo/jdoconfig">

    <!-- Datastore Txn PMF -->
    <persistence-manager-factory name="Datastore">
        <property name="javax.jdo.PersistenceManagerFactoryClass"
            value="org.jpox.jdo.JDOPersistenceManagerFactory"/>
        <property name="javax.jdo.option.ConnectionDriverName"
            value="com.mysql.jdbc.Driver"/>
        <property name="javax.jdo.option.ConnectionURL"
            value="jdbc:mysql://localhost/jpox?useServerPrepStmts=false"/>
        <property name="javax.jdo.option.ConnectionUserName"
            value="jpox"/>
        <property name="javax.jdo.option.ConnectionPassword"
            value=""/>
        <property name="javax.jdo.option.Optimistic"
            value="false"/>
        <property name="org.jpox.autoCreateSchema"
            value="true"/>
    </persistence-manager-factory>

    <!-- Optimistic Txn PMF -->
    <persistence-manager-factory name="Optimistic">
        <property name="javax.jdo.PersistenceManagerFactoryClass"
            value="org.jpox.jdo.JDOPersistenceManagerFactory"/>
        <property name="javax.jdo.option.ConnectionDriverName"
            value="com.mysql.jdbc.Driver"/>
        <property name="javax.jdo.option.ConnectionURL"
            value="jdbc:mysql://localhost/jpox?useServerPrepStmts=false"/>
        <property name="javax.jdo.option.ConnectionUserName"
            value="jpox"/>
        <property name="javax.jdo.option.ConnectionPassword"
            value=""/>
        <property name="javax.jdo.option.Optimistic"
            value="true"/>
        <property name="org.jpox.autoCreateSchema"
            value="true"/>
    </persistence-manager-factory>

</jdoconfig>

So in this example we have 2 named PMFs. The first is known by the name "Datastore" and utilises datastore transactions. The second is known by the name "Optimistic" and utilises optimistic transactions. You simply define all properties for the particular PMF within its specification block.

Instantiating Named PMFs

So in the previous section we defined our named PMFs. So lets instantiate one

PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory("Optimistic");

That's it. The PMF we are returned from JDOHelper will have all of the properties defined in jdoconfig.xml under the name of "Optimistic".