Grails 3 makes it very easy to create a JAR file that is runnable with a simple $java -jar command. We must use the Grails command package or the Gradle task assemble to package our application as a so-called runnable JAR file. This JAR file has all the necessary classes to start up our Grails application.

In the following example we have a Grails application sample-app. We use the Gradle task assemble to package the application into a JAR file. The resulting JAR file can be found in the build/libs directory of our project:

$ gradle assemble
:assetCompile
Processing File 1 of 22 - apple-touch-icon-retina.png
Processing File 2 of 22 - apple-touch-icon.png
Processing File 3 of 22 - favicon.ico
Compressing File 3 of 22 - favicon
Processing File 4 of 22 - grails_logo.png
Processing File 5 of 22 - skin/database_add.png
Processing File 6 of 22 - skin/database_delete.png
Processing File 7 of 22 - skin/database_edit.png
Processing File 8 of 22 - skin/database_save.png
Processing File 9 of 22 - skin/database_table.png
Processing File 10 of 22 - skin/exclamation.png
Processing File 11 of 22 - skin/house.png
Processing File 12 of 22 - skin/information.png
Processing File 13 of 22 - skin/shadow.jpg
Processing File 14 of 22 - skin/sorted_asc.gif
Processing File 15 of 22 - skin/sorted_desc.gif
Processing File 16 of 22 - spinner.gif
Processing File 17 of 22 - application.js
Uglifying File 17 of 22 - application
Compressing File 17 of 22 - application
Processing File 18 of 22 - jquery-2.1.3.js
Uglifying File 18 of 22 - jquery-2.1.3
Compressing File 18 of 22 - jquery-2.1.3
Processing File 19 of 22 - application.css
Minifying File 19 of 22 - application
Compressing File 19 of 22 - application
Processing File 20 of 22 - errors.css
Minifying File 20 of 22 - errors
Compressing File 20 of 22 - errors
Processing File 21 of 22 - main.css
Minifying File 21 of 22 - main
Compressing File 21 of 22 - main
Processing File 22 of 22 - mobile.css
Minifying File 22 of 22 - mobile
Compressing File 22 of 22 - mobile
Finished Precompiling Assets
:buildProperties
:compileJava UP-TO-DATE
:compileGroovy
:processResources
:classes
:compileTestJava UP-TO-DATE
:compileTestGroovy UP-TO-DATE
:processTestResources UP-TO-DATE
:testClasses UP-TO-DATE
:compileIntegrationTestJava UP-TO-DATE
:compileIntegrationTestGroovy UP-TO-DATE
:compileWebappGroovyPages UP-TO-DATE
:compileGroovyPages
:jar
:findMainClass
:startScripts
:distTar
:distZip
:war
:bootRepackage
:assemble

BUILD SUCCESSFUL

Total time: 12.972 secs
$

Next we can run the generated JAR file:

$ java -jar build/libs/sample-app-0.1-jar
Grails application running at http://localhost:8080 in environment: production

We can also use command-line options to set configuration properties. In the following example we start the application on port number 9080:

$ java -jar build/libs/sample-app-0.1-jar --server.port=9080
Grails application running at http://localhost:9080 in environment: production

We can copy this JAR file to another location, for example a test or production server, and use the same command to run our Grails application.

All this works because the bootRepackage task of the Gradle Spring Boot plugin will use the JAR file of the jar task and converts it to a runnable JAR file. The original JAR file is overridden so next time when we execute the assemble task the JAR file is regenerated. To use Gradle's incremental build feature we can configure the bootRepackage task to create a new JAR file instead of overriding the default JAR file. In the following Gradle build script snippet we use a different name for the JAR file that is generated by the bootRepackage task:

...
// Use app classifier for new JAR file.
// For example sample-app-0.1.jar, becomes
// sample-app-0.1-app.jar.
bootRepackage.classifier = 'app'

// Instruct bootRepackage to only use
// JAR file from jar task.
bootRepackage.withJarTask = jar
...

Written with Grails 3.0.9.

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