OSGI Blueprint入门之八

      Blueprint除了组装bean,osgi服务引用等的DI（IOC）功能之外，还可通过各种命名空间（namespace）来扩展。在《Blueprint入门之六》中，我们就用过一个与ConfigAdmin相关的命名空间（http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0）。

      除了ConfigAdmin之外，我们还可以看到aries JPA container提供了JPA相关的blueprint命名空间（http://aries.apache.org/xmlns/jpa/v1.1.0） ，Aries JPA Container根据bundle中的persistence.xml构建持久化域单元（persistence domain unit）后，需要将相应的EntityManagerFactory或EntityManager注入到需要用到该持久化域的bean实例里，就可以使用这个命名空间。
persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name=" com.ponder.myPU " transaction-type="RESOURCE_LOCAL">
    <provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
    <non-jta-data-source>
osgi:service/javax.sql.DataSource/(osgi.jndi.service.name=jdbc/myDS)
</non-jta-data-source>
    <class>com.ponder.*</class>
    <properties>
      <property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema(ForeignKeys=true)"/>
    </properties>
  </persistence-unit>
</persistence>

   注：以上persistence.xml中的（osgi.jndi.service.name=jdbc/myDS）是将注册到jndi的jdbc的数据源注入进来。

   注入EntityManagerFactory：

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:jpa="http://aries.apache.org/xmlns/jpa/v1.1.0" >

  <bean id="processor1" class="com.ponder.processor">
        <jpa:unit property="emf" unitname="com.ponder.myPU" />
    </bean>  
... ....
</blueprint>

   注入EntityManager：

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:jpa="http://aries.apache.org/xmlns/jpa/v1.1.0" >
 <bean id="processor1" class="com.ponder.processor">
        <jpa:context property="em" unitname="com.ponder.myPU" />
    </bean>
... ....
</blueprint>

    在事务(Transaction)方面,Blueprint通过命名空间(xmlns:tx="http://aries.apache.org/xmlns/transactions/v1.0.0)支持声明式事务（Declaractive Transaction）：

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
xmlns:jpa="http://aries.apache.org/xmlns/jpa/v1.0.0"
xmlns:tx="http://aries.apache.org/xmlns/transactions/v1.0.0">
<bean id="processor1" class="com.ponder.processor">
  <jpa:context property="em" unitname="com.ponder.myPU" />
  <tx:transaction method="*" value="Required" />
</bean>
... ...
</blueprint>