EclipseLink/Examples/OSGi/Equinox Byte Code Weaving
In EclipseLink 1.1.2 (Galileo) and above, EclipseLink JPA byte code weaving is supported in Equinox OSGi. Configuration is straight forward and the requirements on your JPA persistence unit bundle are minimal.
Byte code weaving support is implemented through two fragments: org.eclipse.persistence.jpa.equinox.weaving and org.eclipse.persistence.jpa.equinox. o.e.p.j.equinox.weaving is a fragment for the system bundle org.eclipse.osgi. Extending the system bundle is a special case in OSGi and such a fragment is called a framework extension. This extension make use of the Equinox AdaptorHook framework to hook into the byte code loading process and perform weaving when necessary. Configuring a framework extension is done using the standard OSGi osgi.framework.extensions property. This property needs to be declared either in your config.ini or on the commandline as:
o.e.p.j.equinox is a fragment for the org.eclipse.persistence.jpa bundle that registers byte code weavers for persistence units that require it. All that is necessary to enable this is to deploy it with your other bundles.
First create a root folder for the example, we'll refer to it as HOME.
NOTE: This example does not address how to develop an EclipseLink OSGi application in Eclipse PDE. It covers how to configure a runtime environment that supports byte code weaving for EclipseLink JPA. See Developing EclipseLink OSGi in PDE to learn how to develop EclipseLink OSGi applications in Eclipse
- Download Equinox 3.5 to obtain the following bundles and place them in HOME\plugins.
- From the Equinox download page, download the launcher appropriate for your operating system. The launcher comes in two parts: a bundle and a native platform library. Copy both the launcher jar and native library folder to HOME\plugins.
- From an Eclipse 3.5 install's plugins folder copy the following bundle to HOME\plugins:
- Download EclipseLink 1.1.2 (or above) and place the bundles into HOME\plugins
- Download the Apache Derby database bundle org.apache.derby from the Eclipse Orbit download page and place it in HOME\plugins. The Orbit bundle does not contain the client driver so we'll use an embedded database in this example. Note that when using an embedded database only one process can have the database open at a time. Here's an example of the login and config settings for embedded Derby database:
<property name="eclipselink.target-database" value="Derby"/> <property name="eclipselink.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/> <property name="eclipselink.jdbc.url" value="jdbc:derby:comics;create=true"/> <!-- Setting read and write pool mins to 1 will reduce the initial number of connections. --> <property name="eclipselink.jdbc.read-connections.min" value="1"/> <property name="eclipselink.jdbc.write-connections.min" value="1"/>
Enabling Byte Code Weaving in your Application
The following requirements must be met to enable byte code weaving on your Entities:
- Provide class loader to Persistence.createEntityManagerFactory
- Bundle org.eclipse.persistence.jpa must be required by your bundle
- Explicitly indicate you want byte code weaving in your persistence.xml
Passing Class Loader
Access to the classloader that loads your Entities is required by EclipseLink. In your application you need to pass this classloader as a property to Persistence.createEntityManagerFactory(). Failure to provide the classloader will result in a failure.
import org.eclipse.persistence.config.PersistenceUnitProperties; ... Map<String,Object> properties = new HashMap<String, Object>(); properties.put(PersistenceUnitProperties.CLASSLOADER, this.getClass().getClassLoader()); emf = Persistence.createEntityManagerFactory("comics", properties);
In the manifest.mf of your application bundle, you need to require the org.eclipse.persistence.jpa bundle. Note that the minimum version that supports byte code weaving in OSGi is 1.1.2 (Galileo).
... Require-Bundle: org.eclipse.persistence.jpa;bundle-version="1.1.2" ...
Enable Weaving in persistence.xml
Typically, byte code weaving is automatically enabled by EclipseLink based on what environment it's running in. For example, in a Java EE5 container byte code weaving is always enabled. In Equinox, byte code weaving is not automatically enabled. If you have configured your Equinox runtime target correctly, you can go ahead and indicate that you want byte code weaving to be performed.
<property name="eclipselink.weaving" value="true"/>
When running Equinox with a launcher, you can define your configuration in a config.ini file. config.ini should be placed in HOME\configuration. Here are the features of note in the example config.ini below:
- osgi.bundles.defaultStartLevel is set to 6 so that all the bundles that should be started will be started in an unambiguous order.
- osgi.framework.extensions identifies the framework extension org.eclipse.persistence.jpa.equinox.weaving. This is critical for byte code weaving.
- org.eclipse.equinox.common and org.eclipse.update.configurator are started as per the instructions in the Equinox Quickstart.
- javax.persistence is started before org.eclipse.persistence.jpa so that it can start up a service tracker to listen for JPA provider services.
- org.eclipse.persistence.jpa is started before user bundles so that it may register itself as a JPA persistence provider.
- my.example.jpa.bundle (or whatever you call your JPA bundle) is auto-started.
osgi.bundles.defaultStartLevel=6 eclipse.ignoreApp=true osgi.noShutdown=true osgi.framework.extensions=org.eclipse.persistence.jpa.equinox.weaving osgi.bundles= \ org.eclipse.equinox.common@2:start, \ org.eclipse.update.configurator@3:start, \ javax.persistence@4:start, \ org.eclipse.persistence.jpa@5:start, \ org.eclipse.persistence.antlr, \ org.eclipse.persistence.asm, \ org.eclipse.persistence.core, \ org.eclipse.persistence.jpa.equinox, \ my.example.jpa.bundle@start, \ org.apache.derby
With the required bundles in the HOME\plugins folder and config.ini in the HOME\configuration folder you're ready to start your application. On Windows, you can start Equinox by using running the native "launcher.exe" program from the HOME folder. During development it's recommended you run with the "-clean" option to clear caches between runs. The "-console" option can be used to interact with Equinox. This is especially useful when things aren't working as expected.