Donnerstag, 21. November 2013

Gradle Plugin for JPA, JDO, and EBean Bytecode Transformers

The plugin referenced here is meant for use with the tangram framework but there are a few calls which are helpfull for any user of Gradle and
It simply has easy to use wrappers for the enhancer/wever components for the persistence frameworks above since the solutions presented by those projects each for its own reason needed some cosmetic enhancement to fit into my gradle builds.

Prerequisites

Of course you will have some classes with persistence annotations. I'm assuming that you have a (sub)module containing the model classes for the API to be used (JDO, JPA with OpenJPA, DataNucleus, or EclipseLink, or Ebean with JPA annotations) which get compiled by some task of your project.

Preparation

The plugin can be obtained from the tangram snapshots repository.

// build.gradle
buildscript {
  repositories {
    mavenCentral()
    maven { url "http://repository-tangram.forge.cloudbees.com/snapshot" }
  }
  dependencies {
    classpath "tangram:gradle-plugin:0.9-SNAPSHOT"
  }
}


And of course it must be applied

apply plugin: 'tangram'

When using EclipseLink the bytecode transformer called weaver will already be contained in the compile dependencies of your module. The same applies for OpenJPA except that here the bytecode transformer is called enhancer.
For DataNucleus und Ebean the bytecode transformer is called enhancer again and is a dependency of the plugin itself. There is no generic need to have it in the compile dependencies of your module.
So in short, you will not have to modify your dependencies and the resulting package will not contain any additional classes or jars.

Solution

The plugin does not introduce any new tasks but just some methods that can be placed anywhere in the build process. In a standard gradle task-wiring of the java plugin the methods the following locations make sense:

// JDO with DataNucleus
compileJava.doLast {
  nucleusJdoEnhance()
}


// JPA with DataNucleus
compileJava.doLast {
  nucleusJpaEnhance()
}


// JPA with OpenJPA
jar.doFirst {
  openjpaEnhance()
}


// Ebean
compileJava.doLast { 
  ebeanEnhance()
}


// JPA with EclipseLink
compileJava.doLast {

  eclipselinkWeave()
}


But you may decide to use it at other points within your build process.

Background

For OpenJPA the wrapper presented here is a simple wrapper for the ant tasks provided by this project wired up for the given gradle build setup.
For EclipseLink the weaver the jar is included as a dependency for the plugin itself and the weaver is called called via its Java API. So woven codes can be generated independent of the using projects build setup.
For DataNucleus and Ebean the solution is somewhat more complicated since the enhancers are in separate jars which you most likely don't want to include in your resulting packages.
So those jars are also included as a dependency of the plugin, and again the plugin itself calls the Java APIs of the enhancers directly.

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