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Gradle

What is Gradle?

Gradle is a build system That helps your projects and is commonly used with Java projects.

Gradlew and Gradle

Gradle can be intalled on your machine and used to run the different build tasks. However you can include a self contained version of Gradle, Gradlew which can be used without the need to install gradle on the machine.

This guide assumes you are using gradlew

build.gradle

a build.gradle is used for build configurations, add plugins, list library dependencies, and defining tasks.

Useful Gradle Commands

Print out all tasks from the root project

./gradlew tasks

JAVA PROJECTS

For Java Projects you will want to include the following line in your build.gradle file:

apply plugin: 'java'

By adding the Java Plug-in you gain access to additional tasks to build your java project.

if you were to run ./gradlew tasks you will now see the following:

assemble - Assembles the outputs of this project.

build - Assembles and tests this project.

buildDependents - Assembles and tests this project and all projects that depend on it.

buildNeeded - Assembles and tests this project and all projects it depends on.

classes - Assembles main classes.

clean - Deletes the build directory.

jar - Assembles a jar archive containing the main classes.

testClasses - Assembles test classes.

check - Runs all checks.

test - Runs the unit tests.

Majority of the time we will only be concerned with the following.

./gradlew clean

./gradlew build

./gradlew test

you can even run multiple commands in the same line. i.e.

./gradlew clean build

you can even exclude tasks from being executed with

./gradlew -x <task_name>

for example if you were trying to build a jar without running the tests you can execute the following:

./gradlew build -x test

Basic Example

Include in this example is a simple java application which outputs "Hello World!!". This Project uses the build.gradle file to build an executable jar.

Key Points

  • when using the ./gradlew clean build command to build a clean jar, the jar file will be located under /build/libs/<jar_name><version_number>.jar
  • To build an executable jar you need to do one of the following.
  • create a MANIFEST.MF file and point to location of the main class. In our example the contents would look like:
Main-Class: io.pivotal.GradleSample

The MANIFEST.MF is usually create on the following path META-INF/MANIFEST.MF

  • Set the location of the main class in the build.gradle.
jar {
    manifest {
        attributes 'Main-Class': 'io.pivotal.GradleSample'
    }
}
  • you can now build an executable jar with ./gradlew clean build and execute the jar with java -jar buid/libs/<jar_name>.jar