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[[part2_gradle_tasks]]
= Part 2: Running Gradle Tasks

Learn the basics of Gradle tasks by running one and looking at its output.

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

- See available tasks
- Run a task and inspect the results
- Understand tasks
- Explore task dependencies
****

[[part2_begin]]
== Step 0. Before you Begin

1. You initialized your Java app in <<part1_gradle_init.adoc#part1_begin,part 1>>.

== Step 1. Viewing available Tasks
A _task_ is a basic unit of work that can be done by Gradle as part of the build.

In the `tutorial` directory, enter the command below to list all the available tasks in the project:
[source,text]
----
$ ./gradlew tasks
----

The list includes tasks contributed by the `application` plugin and the plugin it applies:

[source,text]
----
Application tasks
-----------------
run - Runs this project as a JVM application

Build tasks
-----------
assemble - Assembles the outputs of this project.
build - Assembles and tests this project.

...

Documentation tasks
-------------------
javadoc - Generates Javadoc API documentation for the main source code.

...

Other tasks
-----------
compileJava - Compiles main Java source.

...
----
A task might be responsible for compilation, copying, and moving files around, creating JAR files, generating Javadoc, publishing artifacts to repositories, or many other discrete units of work.

You can also list the tasks only available in the `app` subproject by running `./gradlew :app:tasks`.

TIP: You can obtain more information in the task listing using the `--all` option: `./gradlew tasks --all`.

In <<part1_gradle_init.adoc#part1_begin,part 1>> of the tutorial, we ran the `build` task using the `./gradlew build` command.

== Step 2. Understanding Tasks
We've listed the tasks available when the project is initialized, but what if we want to create our own tasks?

Gradle provides many _built-in_ tasks that developers can use to enhance build scripts.

This example task copies `*.war` files from the `source` directory to the `target` directory using the `Copy` built-in task.

[source,kotlin]
----
tasks.register<Copy>("copyTask") {
    from("source")
    into("target")
    include("*.war")
}
----

This task, if added to `build.gradle.kts` file in the `app` subproject directory, would be executed using the command `./gradlew :app:copyTask`.

Popular built-in tasks include:

- **Copy** - `Copy` is useful to copy files around.
- **Delete** -  `Delete` is useful to delete files and directories.
- **Exec** - `Exec` is useful to execute arbitrary O/S commands.
- **Zip** - `Zip` is useful to bundle files.

Many more are included in the link:{kotlinDslPath}/gradle/org.gradle.api.tasks/-delete/index.html[DSL documentation].

== Step 3. Understanding Dependencies Between Tasks
Many times, a task requires another task to run first.
If task B uses the output of task A, then task A must complete before task B begins.

- A task may declare its dependencies explicitly.
- A task may depend on other tasks implicitly.

Here is an example of explicit task dependency:
[source,kotlin]
----
tasks.register("hello") {
    doLast {
        println('Hello!')
    }
}

tasks.register("greet") {
    doLast {
        println('How are you?')
    }
    dependsOn("hello")
}
----

In this case, `hello` prints before `greet`. The output is `Hello! How are you?`.

Task execution order is automatically determined by Gradle, taking into account explicit and implicit task dependencies.
If there is no dependency between tasks, Gradle enables users to request a specific execution order.

== Step 4. Viewing Tasks in the IDE
Project tasks are also available in IntelliJ.
The project should be open following <<part1_gradle_init.adoc#part1_begin,part 1>> of the tutorial.

On the right-hand side of your window, open the `Gradle` pane:

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

== Step 5. Running Tasks in the IDE
You can run a Gradle task via IntelliJ by double-clicking that task in the pane.

Double-click **tutorial > app > build > build**.

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

Once the build finishes, make sure it is successful in the IntelliJ console:
[source,text]
----
BUILD SUCCESSFUL in 966ms
7 actionable tasks: 7 executed
3:18:24 AM: Execution finished 'build'.
----

== Step 6. Running Tasks in the Terminal
Run the following command in your terminal:
[source,text]
----
$ ./gradlew build
----
----
> Task :app:compileJava
> Task :app:processResources
> Task :app:classes
> Task :app:jar
> Task :app:startScripts
> Task :app:distTar
> Task :app:distZip
> Task :app:assemble
> Task :app:compileTestJava
> Task :app:processTestResources
> Task :app:testClasses
> Task :app:test
> Task :app:check
> Task :app:build
----
The `build` task uses the source code and its dependencies to build the app.
As seen in the output, the `build` task compiles, assembles, tests, and checks the code.

The tasks are printed in order of execution.
The `jar` tasks is a dependency of the `build` task.

The `jar` task creates an executable JAR file of the app.
Let's run it by itself:
[source,text]
----
$ ./gradlew jar
----
----
> Task :app:compileJava
> Task :app:processResources
> Task :app:classes
> Task :app:jar
----
As expected, the `compileJava` task is a dependency of the `jar` task and executed first.
Once the task finishes, an `app.jar` file is created in your `tutorial/app/build/libs/` folder.

Invoke the `run` task and check the output:
[source,text]
----
$ ./gradlew run
----
----
> Task :app:compileJava
> Task :app:processResources
> Task :app:classes

> Task :app:run
Hello World!

BUILD SUCCESSFUL in 325ms
----

The `run` task executes the code in `tutorial/app/src/main/java/com.gradle.tutorial/App.java`.
The Java code in `App.java` simply prints "Hello World" to the screen:
[source,java]
----
public class App {
    public String getGreeting() {
        return "Hello World!";
    }
    public static void main(String[] args) {
        System.out.println(new App().getGreeting());
    }
}
----

[.text-right]
**Next Step:** <<part3_gradle_dep_man#part3_begin,Dependency Management>> >>
