Java Data Objects

Establish a Datastore Connection and Transaction

Now that our classes have been enhanced, their instances can be stored in a datastore. We now examine how an application establishes a connection with a datastore and executes operations within a transaction. We begin to write software that makes direct use of the JDO interfaces. All JDO interfaces used by an application are defined in the javax.jdo package.

JDO has an interface called PersistenceManager that has a connection with a datastore. A PersistenceManager has an associated instance of the JDO Transaction interface used to control the start and completion of a transaction. The Transaction instance is acquired by calling currentTransaction( ) on the PersistenceManager instance.

Acquiring a PersistenceManager

A PersistenceManagerFactory is used to configure and acquire a PersistenceManager. Methods in the PersistenceManagerFactory are used to set properties that control the behavior of the PersistenceManager instances acquired from the factory. Therefore, the first step performed by a JDO application is the acquisition of a PersistenceManagerFactory instance. To get this instance, call the following static method of the JDOHelper class:

static PersistenceManagerFactory getPersistenceManagerFactory(Properties props);

The Properties instance can be populated programmatically or by loading property values from a property file. Example 1-6 lists the contents of the property file we will use in our Media Mania application. The PersistenceManagerFactoryClass ...