OSGI企业应用与Aries开源项目(2)

    Aries JPA container是一个持久化容器，但它不类似Hibernate，而只是相当于Hibernate的一部分，它还需要如OpenJPA之类的JPA实现的支持，才能真正地完成持久化的工作。

    一个常见的OSGI JPA应用可以是这样的：若干个用JPA的规范编写的实体（Entity），集合在一个Bundle里，并用persistence.xml描述成一个持久化单元（persistence unit）。而persistence.xml里则通过JNDI将JDBC DataSource与该域绑定。最后，Aries JPA container就能将持久化单元的EntityManagerFactory或EntityManager提供给应用来引用。
   
    以下是一个例子：

    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.examples.jpa01PU" 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/jpa01DS)</non-jta-data-source>
    <class>com.ponder.examples.jpa01.CustomerEntity</class>
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
      <property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema(ForeignKeys=true)"/>
    </properties>
  </persistence-unit>
</persistence>

blueprint.xml:

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

    <cm:property-placeholder persistent-id="com.ponder.examples.jpa01">
        <cm:default-properties>
            <cm:property name="DS.DriverName" value="com.mysql.jdbc.Driver" />
            <cm:property name="DS.Url" value="jdbc:mysql://192.168.0.1:3306/mydb" />
            <cm:property name="DS.User" value="user" />
            <cm:property name="DS.Password" value="password" />
            <cm:property name="DS.InitialSize" value="5" />
            <cm:property name="DS.MinIdle" value="5" />
            <cm:property name="DS.MaxIdle" value="20" />
            <cm:property name="DS.MaxWait" value="1000" /> <!-- 1000毫秒 -->
            <cm:property name="DS.MaxActive" value="30" />
            <cm:property name="DS.LogAbandoned" value="true"/>
            <cm:property name="DS.RemoveAbandoned" value="true"/>
            <cm:property name="DS.RemoveAbandonedTimeout" value="180"/> <!-- 180秒 -->
            <cm:property name="DS.TestWhileIdle" value="true"/>
            <cm:property name="DS.TestOnBorrow" value="false"/>
            <cm:property name="DS.TestOnReturn" value="false"/>
            <cm:property name="DS.ValidationQuery" value="SELECT COUNT(0) FROM DUAL"/>
            <cm:property name="DS.ValidationQueryTimeout" value="1"/>
            <cm:property name="DS.TimeBetweenEvictionRunsMillis" value="30000"/>
            <cm:property name="DS.NumTestsPerEvictionRun" value="30"/>
        </cm:default-properties>
    </cm:property-placeholder>
    <bean  id="jpa01DS" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="${DS.DriverName}" />
        <property name="url" value="${DS.Url}" />
        <property name="username" value="${DS.User}" />
        <property name="password" value="${DS.Password}" />
        <property name="initialSize" value="${DS.InitialSize}"/>
        <property name="minIdle" value="${DS.MinIdle}"/>
        <property name="maxIdle" value="${DS.MaxIdle}"/>
        <property name="maxWait" value="${DS.MaxWait}"/>
        <property name="maxActive" value="${DS.MaxActive}"/>
        <property name="logAbandoned" value="${DS.LogAbandoned}"/>
        <property name="removeAbandoned" value="${DS.RemoveAbandoned}"/>
        <property name="removeAbandonedTimeout" value="${DS.RemoveAbandonedTimeout}"/>
        <property name="testWhileIdle" value="${DS.TestWhileIdle}"/>
        <property name="testOnBorrow" value="${DS.TestOnBorrow}"/>
        <property name="testOnReturn" value="${DS.TestOnReturn}"/>
        <property name="validationQuery" value="${DS.ValidationQuery}"/>
        <property name="validationQueryTimeout" value="${DS.ValidationQueryTimeout}"/>
        <property name="timeBetweenEvictionRunsMillis" value="${DS.TimeBetweenEvictionRunsMillis}"/>
        <property name="numTestsPerEvictionRun" value="${DS.NumTestsPerEvictionRun}"/>
    </bean>
    <service ref="jpa01DS" interface="javax.sql.DataSource">
        <service-properties>
            <entry key="osgi.jndi.service.name" value="jdbc/jpa01DS"/>
        </service-properties>
    </service>
</blueprint>

    其中的关键点如下：
    1、持久化单元（PU)定义（persistence.xml)；
    2、数据源（Datasource）：采用apache的dbcp；
    3、blueprint通过placeholder配置DataSource，并发布DataSource服务，并注册到JNDI ；
    4、PU通过jndi引用Datasource；
    5、部署时，karaf通过configAdmin服务将etc/com.ponder.examples.jpa01.cfg的配置信息读入到blueprint的placeholder处。