Part 3: Dependency Management

Learn the basics of project dependencies and Gradle’s dependency management.

In this section you will:

Understand project dependencies
Inspect project dependencies
Use a Build Scan to analyze dependencies
Update project dependencies
Understand transitive dependencies
Adding a version catalog

Step 0. Before you Begin

You initialized your Java app in part 1.
You ran several tasks in part 2.

Step 1. Understanding the Version Catalog

A version catalog is used to declare all direct dependencies of a project in a central location.

It is created by Gradle init in gradle/libs.versions.toml and referenced in subproject build files.

libs.versions.toml

[versions]
guava = "32.1.2-jre"
junit-jupiter = "5.10.0"

[libraries]
guava = { module = "com.google.guava:guava", version.ref = "guava" }
junit-jupiter = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junit-jupiter" }

To reference the libraries defined in the version catalog:

dependencies {
    implementation(libs.guava)
    testImplementation(libs.junit.jupiter)
}

dependencies {
    implementation libs.guava
    testImplementation libs.junit.jupiter
}

In this example, libs.guava and libs.junit.jupiter refer to the corresponding libraries defined in your version catalog.

The libs.junit.jupiter syntax is used because the key contains a hyphen which is a special character.

A version catalog provides a number of advantages over declaring 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.

Step 2. 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(libs.junit.jupiter)

    testRuntimeOnly("org.junit.platform:junit-platform-launcher")

    // This dependency is used by the application.
    implementation(libs.guava)
}

repositories {
    // Use Maven Central for resolving dependencies.
    mavenCentral()
}

dependencies {
    // Use JUnit Jupiter for testing.
    testImplementation libs.junit.jupiter

    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'

    // This dependency is used by the application.
    implementation libs.guava
}

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.

Dependencies - Dependencies declared via configuration types → libs.junit.jupiter and libs.guava

Gradle needs specific information to find a dependency. Let’s look at libs.guava → com.google.guava:guava:32.1.2-jre and libs.junit.jupiter → 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

	Description	com.google.guava:guava:32.1.2-jre	org.junit.jupiter:junit-jupiter-api:5.9.1
Group	identifier of an organization	`com.google.guava`	`org.junit.jupiter`
Name	dependency identifier	`guava`	`junit-jupiter-api`
Version	version # to import	`32.1.2-jre`	`5.9.1`

Group

identifier of an organization

com.google.guava

org.junit.jupiter

Name

dependency identifier

guava

junit-jupiter-api

Version

version # to import

32.1.2-jre

5.9.1

Step 3. 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 4. 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:guava-parent:32.1.2-jre
     |    +--- com.google.code.findbugs:jsr305:3.0.2 (c)
     |    +--- org.checkerframework:checker-qual:3.33.0 (c)
     |    +--- com.google.errorprone:error_prone_annotations:2.18.0 (c)
     |    \--- com.google.j2objc:j2objc-annotations:2.8 (c)
     +--- 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 -> 3.33.0
     +--- com.google.errorprone:error_prone_annotations -> 2.18.0
     \--- com.google.j2objc:j2objc-annotations -> 2.8

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 5. 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 6. Updating Project Dependencies

Adding and changing dependencies is done in the build file and in the version catalog.

Let’s change the guava version and look at how this affects the dependency tree.

Change the guava dependency in the version catalog to:

gradle/libs.version.toml

[versions]
guava = "30.0-jre"
junit-jupiter = "5.10.0"

[libraries]
guava = { module = "com.google.guava:guava", version.ref = "guava" }
junit-jupiter = { module = "org.junit.jupiter:junit-jupiter", version.ref = "junit-jupiter" }

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 7. Run the Java app

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!

Next Step: Applying Plugins >>

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