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Packaging entities
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<persistence> <persistence-unit name = "actionBazaar"> ... </persistence-unit> <persistence-unit name = "humanResources"> ... </persistence-unit> </persistence>
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Persistence unit scoping
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You can define a persistence unit in a WAR, EJB-JAR, or JAR at the EAR level. If you define a persistence unit in a module, it is only visible to that specific module. However, if you define the unit by placing a JAR file in the lib directory of the EAR, the persistence unit will automatically be visible to all modules in the EAR. For this to work, you must remember the restriction that if the same name is used by a persistence unit in the EAR level and at the module level, the persistence unit in the module level will win. Assume you have an EAR file structure like this:
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lib/actionBazaar-common.jar actionBazaar-ejb.jar actionBazaar-web.war
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actionBazaar-common.jar has a persistence unit with the name actionBazaar and actionBazaar-ejb.jar has also a persistence unit with the name actionBazaar.
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The actionBazaar persistence unit is automatically visible to the web module, and you can use as follows:
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@PersistenceUnit(unitName = "actionBazaar") private EntityManagerFactory emf;
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However, if you use this code in the EJB module, the local persistence unit will be accessed because the local persistence unit has precedence. If you want to access the persistence unit defined at the EAR level, you have to reference it with the specific name as follows:
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PersistenceUnit(unitName = "lib/actionBazaar-common.jar#actionBazaar") private EntityManagerFactory emf;
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Again, the name element is important because it is what you use to access the entities. As shown in chapter 9, we use unitName to inject a container-managed EntityManager as follows:
Packaging EJB 3 applications
@PersistenceContext(unitName = "actionBazaar") private EntityManager entityManager;
Refer to the sidebar Persistence unit scoping for more on how a persistence unit is scoped depending on its presence. Specifying the transaction type You can specify transaction-type in persistence.xml (as in listing 11.6) by using the transaction-type attribute. transaction-type can either be JTA or RESOURCE_LOCAL. If you do not specify transaction-type, the container will assume the default transaction-type is JTA. You must utilize JTA as the transaction-type for a persistence unit packaged in a Java EE module. RESOURCE_LOCAL should be specified as a transaction type only when you re exercising JPA outside a Java EE container. As you may recall, we discussed the javax.persistence.EntityTransaction interface in chapter 9; we recommend you avail yourself of EntityTransaction only when you use EJB 3 persistence outside of a Java EE environment. Using a specific persistence provider The provider element specifies the factory class of the EJB 3 persistence provider, such as Hibernate or TopLink. You do not have to specify the persistence provider if you re using the default persistence provider integrated with your Java EE 5 container. For example, if you want Hibernate s persistence provider in the JBoss Application Server or TopLink Essentials persistence provider with Sun GlassFish or the Oracle Application Server, you don t have to define the provider element in persistence.xml. But if you decide to go with the EJB 3 persistence provider from the GlassFish project with either JBoss or Apache Geronimo, then you must specify the provider element as follows:
<provider>oracle.toplink.essentials.PersistenceProvider</provider>
Obviously this example specifies Oracle TopLink as the persistence provider; you can specify the provider element for Hibernate as follows:
<provider>org.hibernate.ejb.HibernatePersistence</provider>
This is helpful when using JPA outside the container. Setting up a DataSource Our entities are persistence objects that access databases. s 7 through 10 discussed how O/R mappings are defined with metadata annotations, and how an
Packaging entities
entity interacts with one or more database tables. We have not, however, broached the subject of how entities interact with a database connection. Back in chapters 3 and 4 we briefly discussed what a DataSource is and how it can be used in an application server by accessing it through JNDI. In addition, you saw examples of session and message-driven beans accessing a DataSource using resource injection. In spite of this, entities cannot use injection, connect to the database themselves, or perform any operation directly; the persistence provider does all that magic behind the scenes. When you persist an instance of an entity, the persistence provider will open or reuse a pooled connection to the database and execute the SQL on your behalf. To configure a persistence unit to connect to a database, you first have to create a DataSource in your Java EE container. For scalability, each DataSource is commonly associated with a connection pool, and the connection pool contains the information for connecting to the database. Configuring an application DataSource Every Java EE application server provides the ability to create and manage DataSources and connection pools. Here is an example of a DataSource and a connection pool used by Sun s GlassFish open source project:
<jdbc-connection-pool connection-validation-method = "auto-commit" datasource-classname = "oracle.jdbc.pool.OracleDataSource" max-pool-size = "32" max-wait-time-in-millis = "60000" name = "ActionBazaarDS" res-type = "javax.sql.DataSource" steady-pool-size = "8"> <property name = "user" value = "ejb3ina"/> <property name = "port" value = "1521"/> <property name = "password" value = "ejb3ina"/> <property name = "networkProtocol" value = "thin"/> <property name = "databaseName" value = "ORCL"/> <property name = "serverName" value = "localhost"/> </jdbc-connection-pool> <jdbc-resource enabled = "true" jndi-name = "jdbc/ActionBazaarDS" pool-name = "ActionBazaarDS"/>
The DataSource uses the JNDI name and connection pool information for the specified database instance. In this example, the DataSource has a jndi-name of jdbc/ActionBazaarDS. Two common naming techniques are to name the pool
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