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connection_pooling_with_jpa_and_karaf

Connection Pooling with JPA and Apache Karaf

This has been tested with Apache Karaf 3.0.3 and by installing the following features:

feature:install scr jpa/2.0.0 openjpa/2.2.2 transaction jndi jdbc

JDBC Driver

PostgreSQL is used in this example. The driver can be retrieved as a bundle from the Apache Servicemix project. Look in the Maven Repository for org.apache.servicemix.bundles.postgresql.

Just drop the bundle into the deploy folder and set the bundle start level to 25.

I think the low bundle level is necessary because it the driver need to be started before the Aries JPA stuff so that it can pick up any Drivers. But I might be wrong with this one.

DataSource

The javax.sql.DataSource instances will be created via Blueprint. Create a OSGI-INF/blueprint/blueprint.xml file in your project which looks like this:

<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" 
	xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.1.0">

    <reference id="transactionManager" interface="javax.transaction.TransactionManager" />
    
    <!-- Configuration Admin suppport -->
    <cm:property-placeholder persistent-id="sdm.persistence.datasource" update-strategy="reload" />

    <bean class="org.postgresql.ds.PGSimpleDataSource" id="sdsDatasource">
        <property name="serverName" value="${host}" />
        <property name="databaseName" value="${database}" />
        <property name="user" value="${user}" />
        <property name="password" value="${password}" />
    </bean>

    <bean class="org.postgresql.xa.PGXADataSource" id="xaDatasource">
        <property name="serverName" value="${host}" />
        <property name="databaseName" value="${database}" />
        <property name="user" value="${user}" />
        <property name="password" value="${password}" />
    </bean>
    
    <bean class="org.apache.commons.dbcp2.managed.BasicManagedDataSource" id="xaSdsDatasource" destroy-method="close">
        <property name="xaDataSourceInstance" ref="xaDatasource" />
        <property name="transactionManager" ref="transactionManager" />
        <property name="maxTotal" value="25" />
        <property name="initialSize" value="3" />
    </bean>
    
    <service id="sdsDS" interface="javax.sql.DataSource" ref="sdsDatasource">
        <service-properties>
             <entry key="osgi.jndi.service.name" value="jdbc/sds" />
        </service-properties>
    </service>

    <service id="xaSdsDS" interface="javax.sql.DataSource" ref="xaSdsDatasource">
        <service-properties>
             <entry key="osgi.jndi.service.name" value="jdbc/xasds" />
        </service-properties>
    </service>
	
</blueprint>

If you have any questions about this file, look at the OSGi Blueprint specs.

BasicManagedDataSource is packaged in the commons-dbcp2 project (which has a dependency to commons-pool2). Both projects are already packaged as bundles and can be fetched from the maven repository.

The placeholders are filled by the ConfigAdmin service. It uses the configuration file sdm.persistence.datasource as stated in the attribute persistent-id which resides in the etc folder of Karaf. It may look something like this:

service.pid=sdm.persistence.datasource
host=server
database=my_db
user=sgbs
password=sgbs

The DataSource instances can be checked via

service:list DataSource

JPA

Now the JPA needs to use our DataSource instances for getting a connection. This can be done in the persistence.xml file.

It may look something like this:

<?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="sdm" transaction-type="JTA">
		<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>

		<jta-data-source>osgi:service/jdbc/xasds</jta-data-source>
		<non-jta-data-source>osgi:service/jdbc/sds</non-jta-data-source>

		<class>my.jpa.EntityClass</class>

		<properties>
			<property name="openjpa.Log" value="File=/tmp/org.apache.openjpa.log, DefaultLevel=TRACE" />
			<property name="openjpa.RuntimeUnenhancedClasses" value="supported" />
		</properties>

	</persistence-unit>

</persistence>

Transaction testing still needs to be done!

Other Solutions

Pax JDBC

The project Pax JDBC offers a nice solution to for creating DataSource objects via ConfigAdmin and also supports connection pooling.

connection_pooling_with_jpa_and_karaf.txt · Last modified: 2015/06/19 15:02 by mihael