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[[part4_gradle_plugins]]
= Part 4: Applying Gradle Plugins

Learn about how plugins extend Gradle's capabilities and use a popular plugin.

****
**In this section you will:**

- Apply a plugin
- Configure the plugin
- Use the plugin
- Explore other plugins
****

[[part4_begin]]
== Step 0. Before you Begin

1. You initialized your Java app in <<part1_gradle_init.adoc#part1_begin,part 1>>.
2. You ran several tasks in <<part2_gradle_tasks#part2_begin,part 2>>.
3. You learned about dependency management in <<part3_gradle_dep_man#part3_begin,part 3>>.

== Step 1. Understanding Plugins

Plugins are the primary method to organize build logic and reuse build logic within a project.

Plugins are also used to distribute custom tasks as packaged code.

Applying a plugin to a project executes code that can create tasks, configure properties, and otherwise extend the project's capabilities. Generally, plugins use the Gradle API to provide additional functionality and extend Gradle's core features.

Plugins can:

- Add tasks to the project (e.g. compile, test).
- Extend the basic Gradle model (e.g. add new DSL elements that can be configured).
- Configure the project, according to conventions (e.g. add new tasks or configure sensible defaults).
- Apply specific configuration (e.g. add organizational repositories or enforce standards).
- Add new properties and methods to existing types via extensions.

== Step 2. Applying a Plugin

Our project currently applies a single plugin, the <<application_plugin#application_plugin,Application Plugin>> which is bundled with Gradle:

====
include::sample[dir="snippets/init/generated/kotlin",files="app/build.gradle.kts[tags=init-plugins]"]
include::sample[dir="snippets/init/generated/groovy",files="app/build.gradle[tags=init-plugins]"]
====

Let's apply a plugin to our project that is maintained and distributed by Gradle called the <<publishing_maven#publishing_maven,Maven Publish Plugin>>.
The Maven Publish Plugin provides the ability to publish build artifacts to an https://maven.apache.org/[Apache Maven repository].
It can also publish to Maven local which is a repository located on your machine.

The default location for Maven local repository may vary but is typically:

- **Mac**: /Users/\[username]/.m2
- **Linux**: /home/\[username]/.m2
- **Windows**: C:\Users\[username]\.m2

A publication destined for a Maven repository normally includes:

- One or more artifacts
- The Gradle Module Metadata
- The Maven POM file

Apply the plugin by adding `maven-publish` to the plugins block in `build.gradle(.kts)`:

====
include::sample[dir="snippets/init/upgraded/kotlin",files="app/build.gradle.kts[tags=init-plugins]"]
include::sample[dir="snippets/init/upgraded/groovy",files="app/build.gradle[tags=init-plugins]"]
====

Don't forget to sync Gradle if you are using IntelliJ IDEA.

Let's make sure the plugin has been applied by looking at the new tasks that are available.

Run `./gradlew :app:tasks` in your command line:

[source,bash]
----
$ ./gradlew :app:tasks
----
[source,text]
----
> Task :app:tasks

------------------------------------------------------------
Tasks runnable from project ':app'
------------------------------------------------------------

...

Publishing tasks
----------------
publish - Publishes all publications produced by this project.
publishToMavenLocal - Publishes all Maven publications produced by this project to the local Maven cache.
----

A new set of publishing tasks are now available called `publish`, and `publishToMavenLocal`.

Similarly, the new tasks from the Maven Publish plugin are now available in IntelliJ in the Gradle right-hand pane.

image::tutorial/intellij-idea-plugin.png[]

== Step 3. Configuring the Plugin

Add the publishing information to your `build.gradle(.kts)` file:

====
include::sample[dir="snippets/init/upgraded/kotlin",files="app/build.gradle.kts[tags=init-publish]"]
include::sample[dir="snippets/init/upgraded/groovy",files="app/build.gradle[tags=init-publish]"]
====

Run `./gradlew :app:tasks` in your command line again, you will see additional tasks now that we have given the plugin additional information about our app:

[source,bash]
----
$ ./gradlew :app:tasks
----
[source,text]
----
> Task :app:tasks

------------------------------------------------------------
Tasks runnable from project ':app'
------------------------------------------------------------

...

Publishing tasks
----------------
generateMetadataFileForMavenPublication - Generates the Gradle metadata file for publication 'maven'.
generatePomFileForMavenPublication - Generates the Maven POM file for publication 'maven'.
publish - Publishes all publications produced by this project.
publishMavenPublicationToMavenLocal - Publishes Maven publication 'maven' to the local Maven repository.
publishToMavenLocal - Publishes all Maven publications produced by this project to the local Maven cache.
----

image::tutorial/intellij-idea-pub.png[]

== Step 4. Using the Plugin

To use the plugin, run the `publishToMavenLocal` task by running `./gradlew :app:publishToMavenLocal`:

[source,bash]
----
$ ./gradlew :app:publishToMavenLocal
----
[source,text]
----
> Task :app:compileJava FROM-CACHE
> Task :app:processResources NO-SOURCE
> Task :app:classes UP-TO-DATE
> Task :app:jar
> Task :app:generateMetadataFileForMavenPublication
> Task :app:generatePomFileForMavenPublication
> Task :app:publishMavenPublicationToMavenLocal
> Task :app:publishToMavenLocal

BUILD SUCCESSFUL in 331ms
----

The `publishToMavenLocal` task builds the POM file and the artifacts to be published.
It then _installs_ them into the local Maven repository.

You can view the POM and GMM file in the `build` directory:

image::tutorial/intellij-idea-dist.png[]

You can also view the files in your Maven Local directory: `~/.m2/repository/com/gradle/tutorial/tutorial/1.0`.

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.gradle.tutorial</groupId>
  <artifactId>tutorial</artifactId>
  <version>1.0</version>
  <packaging>pom</packaging>
</project>
----

== Step 5. Exploring Plugins

Plugins extend Gradle’s capabilities by adding tasks, configurations, and behavior to your build.
They are the **main way to organize and reuse build logic**.

Gradle supports three main plugin types:

1. **Core plugins** – Built into Gradle (e.g., `java`, `application`):
+
[source,kotlin]
----
plugins {
    id("java")
}
----

2. **Community plugins** – Published by others to the link:https://plugins.gradle.org/[Gradle Plugin Portal]:
+
[source,kotlin]
----
plugins {
    id("com.diffplug.spotless") version "6.25.0"
}
----

3. **Custom plugins** – Created by you or your team for internal use. These live in `buildSrc/` or a dedicated subproject.
+
**Convention plugins** are custom plugins used to share common build logic across subprojects (like code style, compiler options, or testing setup):
+
[source,kotlin]
----
plugins {
    id("myproject.java-conventions")
}
----

[TIP]
====
Gradle recommends using convention plugins to avoid duplication and manage shared settings in large builds.
====

[.text-right]
**Next Step:** <<part5_gradle_inc_builds.adoc#part5_begin,Exploring Incremental Builds>> >>
