Gradle

Gradle is an open-source build automation tool focused on flexibility and performance.

Getting Started

Prerequisites

  • JRE >= 1.8
    • java -version
  • Gradle >= 4.10.3
    • gradle -version

Initialize a project

% mkdir basic-demo
% cd basic-demo
% gradle init

What Gradle generated for you

├── build.gradle
├── gradle
│ └── wrapper
│ ├── gradle-wrapper.jar
│ └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
└── settings.gradle
  • build.gradle : Gradle build script for configuring the current project
  • gradle-wrapper.jar: Gradle Wrapper executable JAR
  • gradle-wrapper.properties: Gradle Wrapper configuration properties
  • gradlew: Gradle Wrapper script for Unix-based systems
  • gradlew.bat: Gradle Wrapper script for Windows
  • settings.gradle: Gradle settings script for configuring the Gradle build

Create a task

  1. Create a directory called src.
  2. Add a file called myfile.txt in the src directory. Add the single line Hello, World! to it.
  3. Define a task called copy of type Copy in your build file build.gradle that copied the src directory to a new directory called dest. (You don't have to create the dest directory, the task will do it for you.)
build.gradle
task copy(type: Copy, group: "Custom", description: "Copies sources to the dest directory") {
from "src"
into "dest"
}

Run a task

% ./gradlew copy
> Task :copy
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed

References

Building Java Libraries

Prerequisites

  • JRE >= 1.8
    • java -version
  • Gradle >= 5.0
    • gradle -version

Initialize a library project

From inside the new project directory, run the init task and select java-library project type when prompted.

% mkdir demo
% cd demo
% gradle init
Select type of project to generate:
1: basic
2: cpp-application
3: cpp-library
4: groovy-application
5: groovy-library
6: java-application
7: java-library
8: kotlin-application
9: kotlin-library
10: scala-library
Enter selection (default: basic) [1..10] 7
Select build script DSL:
1: groovy
2: kotlin
Enter selection (default: groovy) [1..2]
Select test framework:
1: junit
2: testng
3: spock
Enter selection (default: junit) [1..3]
Project name (default: demo):
Source package (default: demo):
BUILD SUCCESSFUL in 1s
2 actionable tasks: 2 executed

What Gradle generated for you

├── build.gradle
├── gradle
│ └── wrapper
│ ├── gradle-wrapper.jar
│ └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
├── settings.gradle
└── src
├── main
│ └── java
│ └── demo
│ └── Library.java
└── test
└── java
└── demo
└── LibraryTest.java
  • src/main/java: Default Java source folder
  • src/test/java: Default Java test folder

Review the generated project files

settings.gradle
rootProject.name = 'building-java-libraries'
  • This assigns the name of the project.
build.gradle
plugins {
id 'java-library'
}
repositories {
jcenter()
}
dependencies {
api 'org.apache.commons:commons-math3:3.6.1'
implementation 'com.google.guava:guava:27.0.1-jre'
testImplementation 'junit:junit:4.12'
}
  • repositories: Public Bintray Artifactory repository
  • api 'org.apache.commons:commons-math3:3.6.1': This is an example of a dependency which is exported to consumers, that is to say found on their compile classpath.
  • implementation 'com.google.guava:guava:27.0.1-jre': This is an example of a dependency which is used internally, and not exposed to consumers on their own compile classpath.
  • testImplementation 'junit:junit:4.12': JUnit testing library

Assemble the library JAR

$ ./gradlew build
> Task :compileJava
> Task :processResources NO-SOURCE
> Task :classes
> Task :jar
> Task :assemble
> Task :compileTestJava
> Task :processTestResources NO-SOURCE
> Task :testClasses
> Task :test
> Task :check
> Task :build
BUILD SUCCESSFUL in 11s
4 actionable tasks: 4 executed

You can find your newly packaged JAR file in the build/libs directory with the name building-java-libraries.jar. Verify that the archive is valid by running the following command:

$ jar tf build/libs/building-java-libraries.jar
META-INF/
META-INF/MANIFEST.MF
Library.class

References

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