xjc and schemagen with gradle

In a recent Java project, I need to generate  Java classes from an XML schema and an XML schema from a different set of Java classes. The underlying technology I use for these task is the Java Architecture for XML Binding (JAXB). The jdk comes with two tools, xjc and schemagen (schemagen currently produces a warning that says that it is planned to be replaced by javac in future versions of the jdk, so one should not rely on it. For now, I guess that is ok.). Xjc generates classes from a schema and schemagen generates a schema from a set of annoted classes.

Both generated artifacts might be subject to change, especially the schema. To adapt to that easily, generation is to happen during the build process. I recently started using Gradle, and the following build script is one of  my first exercises with it. The solution rests upon the jaxb-xjc.jar which can be found in maven central. This jar comes with the xjc and schemagen classes. In the build script, I define ant tasks for executing these classes. The ant tasks used come from here. This leaves a straight-forward script (anonymized from my project):

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'application'

mainClassName='my.package.MyMainClass'

defaultTasks 'build'
version = '1.0'
sourceCompatibility = 1.7
schemaTargetDir = new File('generated-sources')

repositories {
 mavenCentral()
}

configurations {
 xjc
}

dependencies {
 xjc group: 'com.sun.xml.bind', name: 'jaxb-xjc', version: '2.2.4-1'
}

task createDirs () {
schemaTargetDir.mkdirs()
}

task xjc () {
 ant.taskdef(name: 'xjc', classname: 'com.sun.tools.xjc.XJCTask', classpath: configurations.xjc.asPath)

 ant.xjc(
  destdir: schemaTargetDir,
  schema: 'src/main/resources/MyInputSchema.xsd'
 )
}

task schemagen () {
 ant.taskdef(name: 'schemagen', classname: 'com.sun.tools.jxc.SchemaGenTask', classpath: configurations.xjc.asPath)

 ant.schemagen(
  srcdir: new File('src/main/java/classes/to/generate/schema/from'),
  destdir: schemaTargetDir
 )
}

xjc.dependsOn createDirs
schemagen.dependsOn createDirs
compileJava.dependsOn xjc, schemagen

Lines 01 through 23 are ‘business as usual’ with a global property and the xjc-dependency. The jaxb-xjc.jar includes both, schemagen and xjc, so a single dependency is sufficient. Lines 24 – 26 define a really simple task for building the necessary directory structure. Lines 28 to 35 and 37 to 44 do the real work. That is, defining the ant task and executing it with the appropriate option. Finally, some task dependency definitions in lines 26 to 48 and the script is done.

Update 16-12-2014: Many thanks to Paweł Grześ for suggesting a modified task definition (see comments). The following example from Pawel generates schemas only if the code has really changed:

task schemagen () {
  inputs.sourceDir('src/main/java/classes/to/generate/schema/from')
  outputs.dir('scr/main/resources/schema')
  doLast {
    ant.taskdef(name: 'schemagen', classname: 'com.sun.tools.jxc.SchemaGenTask', classpath: configurations.xjc.asPath)
    ant.schemagen(
      srcdir: 'src/main/java/classes/to/generate/schema/from',
      destdir: 'scr/main/resources/schema',
      includeAntRuntime: 'false'
    ) {
      schema(file: "mySchema.xsd", namespace: "http://www.myCompany.com")
    }
  }
}

Update 01-08-2016: Lemurian N Mars pointed me to a jaxb plugin that is available for gradle and looks promising. Here is a build script that I modified slightly from Lemurian’s example (stripping Maven/Spring dependencies, streamlining to my example from above) that exemplifies the usage of xjc. I haven’t executed it (yet), so no guarantees that it actually works. Also, I am not sure how to execute schemagen with plugin. Anyways, here is the example:

buildscript {
 repositories {
 jcenter()
}

  dependencies {
    classpath 'com.github.jacobono:gradle-jaxb-plugin:1.3.5'
  }
}

apply plugin: ‘java’

apply plugin: ‘com.github.jacobono.jaxb’

jar {
  baseName = ‘my-project’
  version = ‘0.1.0’
}

repositories {
  jcenter()
}

dependencies {
  jaxb ‘com.sun.xml.bind:jaxb-xjc:2.2.7-b41’
  jaxb ‘com.sun.xml.bind:jaxb-impl:2.2.7-b41’
  jaxb ‘javax.xml.bind:jaxb-api:2.2.7
}

jaxb {
 xjc {
   xsdDir = 'src/main/resources/'
   generatePackage = 'generated-sources'
 }
}