GradleでOpenJPAのenhanceタスクを実装 ref: http://qiita.com/aya_eiya/items/65561d8e534c602818b6

openjpa.gradle

def relativize = {file->
  projectDir.toURI().relativize(file.toURI()).toString()
}

task(enhance,dependsOn:classes) << {
  description 'OpenJPA enhancer task.'
  ant.taskdef (
    name : 'openjpac',
    classpath : project.runtimeClasspath.asPath,
    classname : 'org.apache.openjpa.ant.PCEnhancerTask'
  )
  def resurcesDir = sourceSets.main.output.resourcesDir
  def mainOutDir = relativize(sourceSets.main.output.classesDir)
  def jpacOutDir = relativize(sourceSets.main.output.classesDir) - ~/\/$/+ '_jpa/'
  def orgDir = relativize(sourceSets.main.output.classesDir) - ~/\/$/+ '_org/'
  ant.mkdir(dir:orgDir)
  ant.copy(todir:orgDir){
    fileset(dir:mainOutDir){
      include(name:'**')
    }
  }
  resurcesDir.eachFileRecurse(groovy.io.FileType.FILES) {
    propertiesFile ->
    ant.mkdir(dir:jpacOutDir)
    if(propertiesFile.name ==~ /.*persistence.*\.xml/){
      def propertiesFilePath = relativize(propertiesFile)
      ant.openjpac(
           classpath:project.runtimeClasspath.asPath,
           addDefaultConstructor:true,
           enforcePropertyRestrictions:true,
           directory:jpacOutDir
      ){
        config(propertiesFile:propertiesFilePath)
      }
    }
    ant.move(todir:mainOutDir){
      fileset(dir:jpacOutDir){
        include(name:'**')
      }
    }
    ant.delete(dir:jpacOutDir)
  }
}

jar {
   dependsOn enhance
}