Gradle - FTSRG/cheat-sheets GitHub Wiki

Groovy

On Linux, Gradle does not install a separate Groovy engine. The Ubuntu PPA packages are quite outdated, so the simplest solution is to use sdkman.

Tutorials

• Very good, detailed tutorials
• Vogella tutorial on Gradle
• Vogella tutorial on Groovy

Troubleshooting

Building Groovy script using Grapes & Grab with Gradle

Problem: You're trying to build a Groovy script using Gradle, and the script uses Grapes/Grab to resolve its dependencies. However, gradle build throws an exception (displayed here with gradle build --stacktrace).

* What went wrong:
Execution failed for task ':compileGroovy'.
> org/apache/ivy/core/report/ResolveReport
[...]
* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':compileGroovy'.
[...]
Caused by: java.lang.NoClassDefFoundError: org/apache/ivy/core/report/ResolveReport
	at org.gradle.api.internal.tasks.compile.ApiGroovyCompiler.execute(ApiGroovyCompiler.java:167)
	at org.gradle.api.internal.tasks.compile.ApiGroovyCompiler.execute(ApiGroovyCompiler.java:54)
	at org.gradle.api.internal.tasks.compile.daemon.CompilerDaemonServer.execute(CompilerDaemonServer.java:55)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.messaging.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.messaging.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:364)
	... 2 more
Caused by: java.lang.ClassNotFoundException: org.apache.ivy.core.report.ResolveReport
	... 8 more

Solution: Add the ivy configuration (see the example).

apply plugin: 'groovy'

repositories {
  mavenCentral()
}

configurations {
  ivy
}

dependencies {
  compile group: 'org.codehaus.groovy', name: 'groovy', version: '2.4.6'
  ivy group: 'org.apache.ivy', name: 'ivy', version: '2.4.0'
}

tasks.withType(GroovyCompile) {
  groovyClasspath += configurations.ivy
}

"That said, a better approach is to manage dependencies with Gradle." (Source: http://stackoverflow.com/questions/18173908/error-compiling-a-groovy-project-using-grab-annotation)

So you're generally much better off using Gradle to resolve the dependencies as well:

apply plugin: 'groovy'

dependencies {
  compile localGroovy()
}

sourceSets {
  main {
    groovy {
      srcDir '.'
    }
  }
}

task runScript(dependsOn: 'classes', type: JavaExec) {
  main = 'benchmark'
  classpath = sourceSets.main.runtimeClasspath
}

The localGroovy() dependency places the local Groovy sources to the classpath. The srcDir part sets the source directory to the current directory. To run the script, use the runScript goal:

$ gradle runScript

Sesame cannot find RDF format

Problem:

Exception in thread "main" org.openrdf.rio.UnsupportedRDFormatException: No parser factory available for RDF format Turtle (mimeTypes=text/turtle, application/x-turtle; ext=ttl)

Solution:

As described in the documentation of the Shadow plug-in, simply add:

shadowJar {
  mergeServiceFiles()
}

Re-run Gradle with gradle clean shadowJar.

The related Maven question is discussed on Stack Overflow

Could not create DefaultExternalModuleDependency_Decorated

Problem: the build throws the following error.

* What went wrong:
A problem occurred evaluating project '...'
> Could not create an instance of type org.gradle.api.internal.artifacts.dependencies.DefaultExternalModuleDependency_Decorated.

Solution: this obscure error message is usually caused by writing compile group: instead of compile

So change this:

compile group: "group:artifact:version"

To this:

compile "group:artifact:version"

Include Java/Scala source code in the build

Java

apply plugin: "java"

jar {
  from sourceSets.main.allJava
}

Scala

apply plugin: "scala"

jar {
  from sourceSets.main.allScala
}

Older versions of the Eclipse Buildship plug-in fail on import

• Problem: during import, you may encounter the following error:

  Synchronize Gradle builds with workspace failed due to an unexpected error.
  Unsupported method: HierarchicalEclipseProject.getIdentifier().
  

• Solution #1: click Previous and set the Gradle wrapper's version manually to 3.0 (in our experience, 3.1 and 3.2 do not work).

• Solution #2: update Buildship.

Build errors for IDEA & Scala projects

It seems that there are some compatibility issues in multiple-project builds:

apply plugin: 'idea'
apply plugin: 'scala'

This results in:

* What went wrong:
A problem occurred evaluating project ':...'
> Failed to apply plugin [class 'org.gradle.api.plugins.scala.ScalaBasePlugin']
   > A dependency must not be empty

Solution: remove the idea plugin.

Creating JAR files with all dependencies

If you want to create a JAR file with all dependencies (fat JAR), one option is to use the Shadow plugin. However, it is quite complicated to make it work if you want to define multiple JAR tasks for the same project (e.g., because there are multiple main functions). Another possibility is presented in this tutorial, which does not involve any external dependencies, and it is possible to extend it for multiple JARs in the following way.

First define a function for creating a task.

def createJarTask(def taskName, def mainClass, def jarBaseName) {
    return tasks.create(taskName, Jar) {
    	manifest {
        attributes 'Main-Class': mainClass
	    }
	    baseName = jarBaseName
	    classifier = null
	    version = null
	    from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
	    with jar	    
    }
}

And then call it for each JAR.

createJarTask("jarTask1", "com.example.main1", "main1")
createJarTask("jarTask2", "com.example.main2", "main2")