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<body id="build_docker" class="article">
  <div id="header">
    <h1>Getting Started Building Docker Images with Gradle</h1>
  </div>
  <div id="content">
    <div id="preamble">
      <div class="sectionbody">
        <div class="paragraph">
          <p>We live in a world buzzing full of cloud-native applications. Containerization
            has become a part and parcel of delivering software. What we need to
            provide for is an easy way to deploy an application–what better way than
            Docker images? Fortunately for us, Gradle &amp; the <code>gradle-docker-plugin</code>            can significantly help with this task.</p>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_what_you_ll_build">What you&#8217;ll build</h2>
      <div class="sectionbody">
        <div class="ulist">
          <ul>
            <li>
              <p>A sample Docker image that you can additionally opt to push to the
                Docker registry.</p>
            </li>
          </ul>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_what_you_ll_need">What you&#8217;ll need</h2>
      <div class="sectionbody">
        <div class="ulist">
          <ul>
            <li>
              <p>A text editor</p>
            </li>
            <li>
              <p>A command prompt</p>
            </li>
            <li>
              <p>The Java Development Kit (JDK), version 1.8 or higher</p>
            </li>
            <li>
              <p>A <a href="https://gradle.org/install">Gradle distribution</a>, version
                5.2 or better</p>
            </li>
            <li>
              <p><a href="https://www.docker.com/">Docker</a></p>
            </li>
            <li>
              <p><a href="https://bmuschko.github.io/gradle-docker-plugin/current/user-guide/">Gradle Docker Plugin</a></p>
            </li>
          </ul>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_create_a_project_folder">Create a project folder</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>The first step is to create a folder for the new project and change directory
            into it.</p>
        </div>
        <div class="listingblock terminal sample-command">
          <div class="content">
            <pre>$ mkdir docker
$ cd docker</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_run_the_init_task">Run the Init Task</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>From inside the new project directory, run the init task using the <code>gradle init</code>            command in the terminal.</p>
        </div>
        <div class="listingblock terminal sample-command">
          <div class="content">
            <pre>$ gradle init

Select type of project to generate:
  1: basic
  2: application
  3: library
  4: Gradle plugin
Enter selection (default: basic) [1..4] 2

Select implementation language:
  1: C++
  2: Groovy
  3: Java
  4: Kotlin
  5: Scala
  6: Swift
Enter selection (default: Java) [1..6] 3

Split functionality across multiple subprojects?:
  1: no - only one application project
  2: yes - application and library projects
Enter selection (default: no - only one application project) [1..2] 1

Select build script DSL:
  1: Groovy
  2: Kotlin
Enter selection (default: Groovy) [1..2] 1

Generate build using new APIs and behavior (some features may change in the next minor release)? (default: no) [yes, no]
Select test framework:
  1: JUnit 4
  2: TestNG
  3: Spock
  4: JUnit Jupiter
Enter selection (default: JUnit Jupiter) [1..4] 1

Project name (default: docker):
Source package (default: docker..java):

&gt; Task :init
Get more help with your project: https://docs.gradle.org/7.4.1/samples/sample_building_java_applications.html

BUILD SUCCESSFUL in 29s
2 actionable tasks: 2 executed</pre>
          </div>
        </div>
        <div class="paragraph">
          <p>The init task generates the new project with the following structure:</p>
        </div>
        <div class="listingblock">
          <div class="content">
            <pre>docker
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── app
|   ├── build.gradle
│   └── src
│       └── main
|       |   └── java
|       |       └── App.java
|       ├── test
|       |   └── java
|       |       └── AppTest.java
│       └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
└── settings.gradle</pre>
          </div>
        </div>
        <div class="olist arabic">
          <ol class="arabic">
            <li>
              <p>Generated folder for wrapper files</p>
            </li>
            <li>
              <p>Gradle wrapper start scripts</p>
            </li>
            <li>
              <p>Settings file to define build name and subprojects</p>
            </li>
            <li>
              <p>Build script of lib project</p>
            </li>
            <li>
              <p>./app folder containing the Java application</p>
            </li>
          </ol>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_build_the_project">Build the project</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>To build the project, we levy the <code>build</code> command.</p>
        </div>
        <div class="listingblock terminal sample-command">
          <div class="content">
            <pre>$ ./gradlew build

BUILD SUCCESSFUL
7 actionable tasks: 7 executed</pre>
          </div>
        </div>
        <div class="paragraph">
          <p>The project provides the <a href="gradle_wrapper.html#gradle_wrapper">Gradle Wrapper</a>            as part of the repository. It is a recommended practice for any Gradle
            project as it enables your project to built on CI without having to install
            the Gradle runtime.</p>
        </div>
        <div class="listingblock terminal sample-command">
          <div class="content">
            <pre>$ ./gradlew build --scan
Publishing build scan...
https://gradle.com/s/xxxxxxx</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_add_a_plugin_entry_to_build_gradle">Add a plugin entry to build.gradle</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>We make use of the 'docker-java-application' plugin here to carry out the
            essential task of building the Docker image.</p>
        </div>
        <div class="listingblock">
          <div class="content">
            <pre>plugins {
    id 'application'

    id 'java'
    id 'com.bmuschko.docker-java-application' version '7.3.0'
    // mentioning a compatible version is a must
}</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_run_gradle_tasks_command">Run Gradle tasks command</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>With this command, gradle picks up the tasks related to Docker. We can
            verify the same by running the <code>tasks</code> task of the gradle
            wrapper.</p>
        </div>
        <div class="listingblock terminal">
          <div class="content">
            <pre>❯ ./gradlew tasks

&gt; Task :tasks

------------------------------------------------------------
Tasks runnable from root project 'docker'
------------------------------------------------------------

...

Docker tasks
------------
dockerBuildImage - Builds the Docker image for the application.
dockerCreateDockerfile - Creates the Docker image for the application.
dockerPushImage - Pushes created Docker image to the repository.
dockerSyncBuildContext - Copies the distribution resources to a temporary directory for image creation.

...

[listing.terminal]</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_generating_a_dockerfile_optional">Generating a Dockerfile (optional)</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>As an optional step, we can generate and inspect the Dockerfile which is
            generated on levying the <code>dockerCreateDockerfile</code> command:</p>
        </div>
        <div class="listingblock">
          <div class="content">
            <pre>FROM openjdk:11-jre-slim
LABEL maintainer=codespace
WORKDIR /app
COPY libs libs/
COPY classes classes/
ENTRYPOINT ["java", "-cp", "/app/resources:/app/classes:/app/libs/*", "docker.java.App"]
EXPOSE 8080</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_building_the_docker_image">Building the Docker image</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>To build the Docker image, we carry out the <code>dockerBuildImage</code>            task. This step will auto-generate the Dockerfile and create the image
            for us.</p>
        </div>
        <div class="listingblock terminal">
          <div class="content">
            <pre>$ ./gradlew dockerBuildImage

&gt; Task :app:dockerBuildImage
Building image using context '/workspaces/testing-gradle/app/build/docker'.
Using images 'docker-getting-started-gradle-java/app:latest'.
Step 1/7 : FROM openjdk:11-jre-slim
 ---&gt; d3b5993fad1f
Step 2/7 : LABEL maintainer=codespace
 ---&gt; Running in 4c9a751ea6c1
Removing intermediate container 4c9a751ea6c1
 ---&gt; 3d951b688e90
Step 3/7 : WORKDIR /app
 ---&gt; Running in ede4f9b275d8
Removing intermediate container ede4f9b275d8
 ---&gt; cddca74203de
Step 4/7 : COPY libs libs/
 ---&gt; fca50e87d768
Step 5/7 : COPY classes classes/
 ---&gt; 5a91c294d8d2
Step 6/7 : ENTRYPOINT ["java", "-cp", "/app/resources:/app/classes:/app/libs/*", "docker.java.App"]
 ---&gt; Running in d1c53fba1df3
Removing intermediate container d1c53fba1df3
 ---&gt; b7ef69af5fd3
Step 7/7 : EXPOSE 8080
 ---&gt; Running in 07e2d60733b2
Removing intermediate container 07e2d60733b2
 ---&gt; f9d090080e8a
Successfully built f9d090080e8a
Successfully tagged docker/app:latest
Created image with ID 'f9d090080e8a'.</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_run_the_docker_image">Run the Docker image</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>The generated Docker image can be run via the Docker CLI command <code>docker run</code>            by providing the image ID.</p>
        </div>
        <div class="listingblock terminal">
          <div class="content">
            <pre>$ docker run --rm f9d090080e8a
Hello World!</pre>
          </div>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_push_the_docker_image_to_registry_optional">Push the Docker image to registry (optional)</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>We can also opt to push to a registry of our choice by levying the <code>dockerPushImage</code>            command.</p>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_summary">Summary</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>That’s it! You’ve successfully built &amp; run a Docker image with the
            help of the <code>gradle-docker-plugin</code>. You’ve learned how to:</p>
        </div>
        <div class="ulist">
          <ul>
            <li>
              <p>Initialize a project that produces a Java application</p>
            </li>
            <li>
              <p>Run the build and view the test report</p>
            </li>
            <li>
              <p>Install the <code>gradle-docker-plugin</code></p>
            </li>
            <li>
              <p>Run the Gradle tasks command to verify</p>
            </li>
            <li>
              <p>Generate the Dockerfile</p>
            </li>
            <li>
              <p>Build the Docker image</p>
            </li>
            <li>
              <p>Run the Docker image</p>
            </li>
            <li>
              <p>Push the Docker image to a registry</p>
            </li>
          </ul>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_further_reading">Further reading</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>You can learn more about advanced Docker usage through these resources:</p>
        </div>
        <div class="ulist">
          <ul>
            <li>
              <p><a href="https://dockerlabs.collabnix.com/docker/cheatsheet/">The  Ultimate Docker Cheat Sheet</a></p>
            </li>
            <li>
              <p><a href="https://docs.docker.com/engine/reference/run/">Docker Run Reference</a></p>
            </li>
            <li>
              <p><a href="https://docs.docker.com/get-started/">Getting Started with Docker</a></p>
            </li>
            <li>
              <p><a href="https://aws.amazon.com/docker/">What is Docker?</a></p>
            </li>
            <li>
              <p><a href="https://www.docker.com/resources/what-container">Containerisation &amp; Docker</a></p>
            </li>
          </ul>
        </div>
      </div>
    </div>
    <div class="sect1">
      <h2 id="_next_steps">Next steps</h2>
      <div class="sectionbody">
        <div class="paragraph">
          <p>Building a Docker image may seem like a trivial task, but for advanced
            use cases you can check out:</p>
        </div>
        <div class="ulist">
          <ul>
            <li>
              <p><a href="https://bmuschko.github.io/gradle-docker-plugin/#provided_plugins">Provided plugins by gradle-docker-plugin</a></p>
            </li>
            <li>
              <p><a href="https://mvnrepository.com/artifact/com.bmuschko/gradle-docker-plugin">gradle-docker-plugin artifact</a></p>
            </li>
            <li>
              <p><a href="https://github.com/palantir/gradle-docker">Palantir plugin</a></p>
            </li>
          </ul>
        </div>
      </div>
    </div>
  </div>
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