spiros.blog()Spiros Tzavellas’s blog, mostly on software development and Java.

EclipseLink provides advanced JPA features such as lazy-loading, change tracking and fetch groups using bytecode weaving. To use bytecode weaving you can either dynamically instrument your entity classes at runtime (via a jvm agent) or use a tool to statically process the .class files after compilation. In this post we will present how to use EclipseLink’s static weaver in a Maven project.

To enable static weaving in a Maven based project we have to add the Eclipselink weaver in the process-classes phase of the Maven’s build life cycle. The process-classes phase happens after the compile phase and allows the post-processing of files generated in compile phase. In our case, the EclipseLink weaver will post-process the .class files produced by the compiler to add extra bytecodes that implement the desired JPA functionality (lazy-loading, etc).

In the below code we use the Maven AntRun plugin to call (via the java ANT task) the command line version of the EclipseLink’s static weaver. Please note that the class name of the weaver is org.eclipse.persistence.tools.weaving.jpa.StaticWeave and not org.eclipse.persistence.tools.weaving.StaticWeave as the EclipseLink JPA Extensions wiki page says.

<build>
 <plugins>
   <plugin>
     <artifactId>maven-antrun-plugin</artifactId>
     <executions>
       <execution>
         <phase>process-classes</phase>
         <configuration>
           <tasks>
             <java classname="org.eclipse.persistence.tools.weaving.jpa.StaticWeave"
                   classpathref="maven.runtime.classpath" fork="true">
               <arg line="-loglevel FINE -persistenceinfo src/main/resources target/classes target/classes"/>
             </java>
           </tasks>
         </configuration>
         <goals>
           <goal>run</goal>
         </goals>
       </execution>
     </executions>
   </plugin>
 </plugins>
</build>

In addition to the pom.xml changes in order to use static weaving in EclipseLink you have to set the eclipselink.weaving property to static in the META-INF/peristence.xml file.

<property name="eclipselink.weaving" value="static" />

For more information about EclipseLink’s static weaving see the How to Configure Static Weaving for JPA Entities section of the Using EclipseLink JPA Extensions wiki page.

The EclipseLink/Maven wiki page of the EclipseLink project has information on how to setup your Maven dependencies in order to use EclipseLink in a Maven based project. The problem with that page is that it contains typos in all artifactIds of the OSGi enabled artifacts. For example the page lists org.eclipse.peristence.jpa as the artifactId of the JPA bundle instead of org.eclipse.persistence.jpa. Below I have the code that you have to add to your pom.xml in order to use EclipseLink as a JPA provider in your project.

First include the EclipseLink repository in your Maven repositories by adding the following XML snippet.

<repositories>
  <repository>
    <id>EclipseLink</id>
    <url>http://www.eclipse.org/downloads/download.php?r=1&amp;nf=1&amp;file=/rt/eclipselink/maven.repo</url>
  </repository>
</repositories>

Then add the following dependencies in the dependencies section of pom.xml

<dependency>
  <groupId>org.eclipse.persistence</groupId>
  <artifactId>org.eclipse.persistence.jpa</artifactId>
  <version>1.0.1</version>
  <scope>runtime</scope>
</dependency>
<dependency>
  <groupId>org.eclipse.persistence</groupId>
  <artifactId>org.eclipse.persistence.core</artifactId>
  <version>1.0.1</version>
  <scope>runtime</scope>
</dependency>
<dependency>
  <groupId>org.eclipse.persistence</groupId>
  <artifactId>org.eclipse.persistence.asm</artifactId>
  <version>1.0.1</version>
  <scope>runtime</scope>
</dependency>
<dependency>
  <groupId>org.eclipse.persistence</groupId>
  <artifactId>org.eclipse.persistence.antlr</artifactId>
  <version>1.0.1</version>
  <scope>runtime</scope>
</dependency>

Remember that the above dependencies are for using EclipseLink as a JPA provider. You might also need to include the MOXY or the SDO bundle if you want to use XML mapping or SDO. Also if you want to use EclipseLink’s JPA extensions in your code (like the @Cache annotation for example) change the scope of the org.eclipse.persistence.jpa artifact from runtime to compile.