# Part 7: Writing Plugins

version 9.0.0

Learn the basics of writing and applying Gradle plugins.

In this section, you will:

- Add a custom task to the Plugin

- Apply the Plugin to a subproject

- Use the Plugin

## Step 0. Before you Begin

1. You initialized your Java app in part 1.

2. You understand the Gradle Build Lifecycle from part 2.

3. You added a subproject and a separate Build in part3.

4. You viewed a Settings file in part 4.

5. You authored a Build script in part 5.

6. You authored a Task in part 6.

## Step 1. Develop the Plugin

Let’s tie our custom `LicenseTask` to our plugin.

Update the `LicensePlugin` with the code for the `Plugin` below (don’t change anything else in the file):

gradle/license-plugin/plugin/src/main/kotlin/license/LicensePlugin.kt

    class LicensePlugin: Plugin<Project> {
        override fun apply(project: Project) {
            project.tasks.register("license", LicenseTask::class.java) { task ->
                task.description = "add a license header to source code"   // Add description
                task.group = "from license plugin"                         // Add group
            }
        }
    }

gradle/license-plugin/plugin/src/main/kotlin/license/LicensePlugin.groovy

    class LicensePlugin implements Plugin<Project> {
        void apply(Project project) {
            project.tasks.register("license", LicenseTask) { task ->
                task.setDescription("add a license header to source code")  // Add description
                task.setGroup("from license plugin")                        // Add group
            }
        }
    }

## Step 2. Add a license.txt file

Add a file called `license.txt` to the root directory of the project and add the following text to it:

license.txt

    /*
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

## Step 3. Apply the Plugin

Apply the plugin to the `app` subproject (if not done already):

app/build.gradle.kts

    plugins {
        application
        id("com.tutorial.license") // Apply custom plugin
    }

app/build.gradle

    plugins {
        id 'application'
        id('com.tutorial.license') // Apply custom plugin
    }

Make sure the plugin is correctly applied by listing the available tasks in the `app` subproject:

    $ ./gradlew :app:tasks

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

    ...

    From license plugin tasks
    -------------------------
    license - add a license header to source code

## Step 4. Run the custom Task

Finally, it’s time to run the new task.

First, let’s inspect some source code:

app/src/main/java/authoring/tutorial/App.java

    package authoring.tutorial;

    import com.gradle.CustomLib;

    public class App {
        public String getGreeting() {
            return "CustomLib identifier is: " + CustomLib.identifier;
        }

        public static void main(String[] args) {
            System.out.println(new App().getGreeting());
        }
    }

Next, let’s run the task with `./gradlew :app:license`:

    $ ./gradlew :app:license

    > Task :license-plugin:plugin:compileKotlin UP-TO-DATE
    > Task :license-plugin:plugin:compileJava NO-SOURCE
    > Task :license-plugin:plugin:pluginDescriptors UP-TO-DATE
    > Task :license-plugin:plugin:processResources UP-TO-DATE
    > Task :license-plugin:plugin:classes UP-TO-DATE
    > Task :license-plugin:plugin:jar UP-TO-DATE

    > Configure project :app

    > Task :app:license

    BUILD SUCCESSFUL in 410ms
    5 actionable tasks: 1 executed, 4 up-to-date

Now inspect the same source code, which should include a license header:

app/src/main/java/authoring/tutorial/App.java

    /*
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    package authoring.tutorial;

    import com.gradle.CustomLib;

    public class App {
        public String getGreeting() {
            return "CustomLib identifier is: " + CustomLib.identifier;
        }

        public static void main(String[] args) {
            System.out.println(new App().getGreeting());
        }
    }

Congratulations, you have completed the tutorial!

## Step 4. Next steps

We recommend going through each section of the User Manual.

Next Step: Structuring Builds >>