Part 3: Dependency Management
Learn the basics of project dependencies and Gradle’s dependency management.
Step 1. Understanding Project Dependencies
Gradle provides excellent support for dependency management and automation.
Let’s take another look at our build script (the build.gradle.kts file), specifically the following section:
repositories {
// Use Maven Central for resolving dependencies.
mavenCentral()
}
dependencies {
// Use JUnit Jupiter for testing.
testImplementation("org.junit.jupiter:junit-jupiter:5.9.1")
// This dependency is used by the application.
implementation("com.google.guava:guava:32.1.2-jre")
}
Some key concepts in Gradle dependency management include:
Repositories - The source of dependencies → mavenCentral()
Maven Central is a collection of jar files, plugins, and libraries provided by the Maven community and backed by Sonatype. It is the de-facto public artifact store for Java and is used by many build systems.
Gradle needs specific information to find a dependency.
Let’s look at com.google.guava:guava:32.1.2-jre and org.junit.jupiter:junit-jupiter-api:5.9.1; they are broken down as follows:
| Description | com.google.guava:guava:32.1.2-jre | org.junit.jupiter:junit-jupiter-api:5.9.1 | |
|---|---|---|---|
Group |
identifier of an organization |
|
|
Name |
dependency identifier |
|
|
Version |
version # to import |
|
|
Step 2. Understanding Transitive Dependencies
A transitive dependency is a dependency of a dependency.
For our guava dependency to work, it requires a library called failureaccess.
Therefore failureaccess is a transitive dependency of the project.
Step 3. Viewing Project Dependencies
You can view your dependency tree in the terminal using the ./gradlew :app:dependencies command:
$ ./gradlew :app:dependencies
> Task :app:dependencies
------------------------------------------------------------
Project ':app'
------------------------------------------------------------
...
compileClasspath - Compile classpath for source set 'main'.
\--- com.google.guava:guava:32.1.2-jre
+--- com.google.guava:failureaccess:1.0.1
+--- com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava
+--- com.google.code.findbugs:jsr305:3.0.2
+--- org.checkerframework:checker-qual:3.12.0
+--- com.google.errorprone:error_prone_annotations:2.11.0
\--- com.google.j2objc:j2objc-annotations:1.3
...
The output clearly depicts that com.google.guava:guava:32.1.2-jre has a dependency on com.google.guava:failureaccess:1.0.1.
Step 4. Viewing Dependencies in a Build Scan®
To view dependencies using a Build Scan, run the build task with an optional --scan flag.
In the tutorial directory, enter the command below and follow the prompt to accept the terms:
$ ./gradlew build --scan
BUILD SUCCESSFUL in 423ms
7 actionable tasks: 7 up-to-date
Publishing a build scan to scans.gradle.com requires accepting the Gradle Terms of Service defined at https://gradle.com/terms-of-service. Do you accept these terms? [yes, no] yes
Gradle Terms of Service accepted.
Publishing build scan...
https://gradle.com/s/link
A Build Scan is a shareable and centralized record of a build and is available as a free service from Gradle.
Click the link provided in the prompt: https://gradle.com/s/link.
| You will have to accept the terms of service to use Build Scans. |
You will need to activate the Build Scan by using your email:
You will receive the final link to the scan in your inbox which should look as follows:
Open the Dependencies tab in the menu and expand compileClasspath, runtimeClasspath, testCompileClasspath, and testRuntimeClasspath:
As expected, we can see the declared dependencies junit and guava are used by Gradle to compile, run, and test the app.
Expand com.google.guava:guava:32.1.2-jre and org.junit.jupiter:junit-jupiter:5.9.1 in the window:
There are several transitive dependencies under junit and guava.
For example, the com.google.code.findbugs:jsr305:3.0.2 transitive dependency comes from the com.google.guava:guava:32.1.2-jre dependency.
Step 5. Updating Project Dependencies
Adding and changing dependencies is done in the build file.
Let’s change the guava version and look at how this affects the dependency tree.
Change the guava dependency to the gradle.build.kts file to:
implementation("com.google.guava:guava:30.0-jre")
If you change the file using IntelliJ, don’t forget to click the sync Gradle button:
Run ./gradlew build --scan and view the Build Scan results:
Run ./gradlew :app:dependencies in the terminal to check the changes in the dependency tree:
compileClasspath - Compile classpath for source set 'main'.
\--- com.google.guava:guava:30.0-jre
+--- com.google.guava:failureaccess:1.0.1
+--- com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava
+--- com.google.code.findbugs:jsr305:3.0.2
+--- org.checkerframework:checker-qual:3.5.0
+--- com.google.errorprone:error_prone_annotations:2.3.4
\--- com.google.j2objc:j2objc-annotations:1.3
...
It is clear the guava dependency has been updated to version 30.0 and the transitive dependencies have changed as well.
Step 6. Adding a Version Catalog
A version catalog is used to declare all direct dependencies of a project in a central location.
It is created in gradle/libs.versions.toml and referenced in subproject build files.
First, create the libs.versions.toml file in the gradle directory.
Then, add the following lines to this new file:
[versions]
junitVer = "5.9.1"
guavaVer = "32.1.2-jre"
[libraries]
junit = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junitVer" }
guava = { module = "com.google.guava:guava", version.ref = "guavaVer" }
In your app/build.gradle.kts file, update the dependency block accordingly:
dependencies {
testImplementation(libs.junit)
implementation(libs.guava)
}
Run ./gradlew build to make sure the changes take effect.
Finally, make sure everything is working using the run task, either in your terminal or IDE:
./gradlew run > Task :app:compileJava UP-TO-DATE > Task :app:processResources NO-SOURCE > Task :app:classes UP-TO-DATE > Task :app:run Hello World!
A version catalog provides a number of advantages over declaring the dependencies directly in build scripts:
-
Gradle generates type-safe accessors from the catalog so that you can easily add dependencies with autocompletion in the IDE.
-
It is a central place to declare a version of a dependency so that any changes apply to every subproject.
Next Step: Applying Plugins >>