Build, test, and containerize Java applications

This page explains how to use Cloud Build to build, test, and containerize Java-based applications, upload your container images to Artifact Registry, and generate build provenance.

Before you begin

• Be familiar with creating Java-based applications.
• Have your Java project ready, including a Dockerfile.
• Have a Docker repository in Artifact Registry, or create a new repository.
• Be familiar with how to write a Cloud Build configuration file.
• To run the gcloud commands in this page, install the Google Cloud CLI.

Using the maven or gradle image

You can configure Cloud Build to build Java applications using the maven image or the gradle image from Docker Hub.

maven

To execute your tasks in the maven image, add a step to your build config with the following fields:

• name: Set the value of this field to maven or maven:<tag>, where the tag represents the version. If you don't specify the image tag, Cloud Build uses the latest image by default.
• entrypoint: Setting this field overrides the default entry point of the image referenced in name. Set the value of this field to mvn to invoke mvn as the entrypoint of the build step and run mvn commands.
• args: The args field of a build step takes a list of arguments and passes them to the image referenced by the name field.

The following build step specifies the entrypoint for the maven image tagged as 3.3-jdk-8 and prints the build tool version:

steps:
- name: maven:3.3-jdk-8
  entrypoint: mvn
  args: ['--version']

gradle

To execute your tasks in the gradle image, add a step to your build config with the following fields:

• name: Set the value of this field to gradle or gradle:<tag>, where the tag represents the version. If you don't specify the image tag, Cloud Build uses the latest image by default.
• entrypoint: Setting this field overrides the default entry point of the image referenced in name. Set the value of this field to gradle to invoke gradle as the entrypoint of the build step and run gradle commands.
• args: The args field of a build step takes a list of arguments and passes them to the image referenced by the name field.

The following build step specifies the entrypoint for the gradle image tagged as 5.6.2-jdk8 and prints the build tool version:

steps:
- name: gradle:5.6.2-jdk8
  entrypoint: gradle
  args: ['--version']

Configuring Java builds

1. In your project root directory, create a build config file named cloudbuild.yaml.

2. Run tests: maven and gradle provide maven test and gradle test, which downloads dependencies, builds the applications, and runs any tests specified in your source code. The args field of a build step takes a list of arguments and passes them to the image referenced by the name field.

   In your build config file, add test to the args field to invoke test within maven and gradle:

   maven

   steps:
   - name: maven:3.3-jdk-8
     entrypoint: mvn
     args: ['test']
   

   gradle

   steps:
   - name: gradle:5.6.2-jdk8
     entrypoint: gradle
     args: ['test']
   

3. Package application: To package your application into a JAR file for your maven image, specify the package command in the args field. The package command builds a JAR file in /workspace/target/.

   To package your application into a JAR file for your gradle image, specify the assemble command in the args field. The assemble command builds a JAR file in workspace/build/libs.

   The following build step packages your Java application:

   maven

   steps:
   - name: maven:3.3-jdk-8
     entrypoint: mvn
     args: ['package','-Dmaven.test.skip=true']
   

   Note: The package command re-runs tests. Adding -Dmaven.test.skip=true to the args field will skip tests.

   gradle

   steps:
   - name: gradle:5.6.2-jdk8
     entrypoint: gradle
     args: ['assemble']
   

4. Containerize application: Cloud Build provides a prebuilt Docker image that you can use to containerize your Java application. To containerize your Java application, in your build config file:

   • Add a name field and specify the prebuilt Docker image at gcr.io/cloud-builders/docker.
   • Add an args field and specify the build arguments, including the name of the container image to build, and the path to your build artifact.
   • Add an images field to push the built container image to Artifact Registry.

   • Optional: Add requestedVerifyOption: VERIFIED within the options field in your build config file to enable Supply chain Levels for Software Artifacts (SLSA) provenance generation.

     Note: If you use a docker push build step to upload images to Artifact Registry rather than using the images field, then your build won't have provenance information.

   The following build step containerizes your application, pushes your container image to Artifact Registry, and generates build provenance information:

   maven

   steps:
   - name: gcr.io/cloud-builders/docker
     args: ['build', '-t', 'location-docker.pkg.dev/project-id/repository/image', '--build-arg=JAR_FILE=target/build-artifact', '.']
   images: ['location-docker.pkg.dev/project-id/repository/image']
   

   gradle

   steps:
   - name: gcr.io/cloud-builders/docker
     args: ['build', '-t', 'location-docker.pkg.dev/project-id/repository/image', '--build-arg=JAR_FILE=build/libs/build-artifact', '.']
   images: ['location-docker.pkg.dev/project-id/repository/image']
   

   Where:

   • location: the regional or multi-regional location for your repository.
   • project-id: the ID of your Google Cloud project.
   • repository: the name of your repository Artifact Registry.
   • image: the name of your container image.
   • build-artifact: the name of your JAR file created from your build step.

5. Start your build: When you have your build config file ready, start your build by entering the following command in your terminal:

   gcloud builds submit --region=REGION --config config-file-path source-directory
   

   Where:

   • config-file-path: the path to your build config file. In this example, the build config file is named cloudbuild.yaml.
   • source-directory: the path or URL to your source code.
   • REGION: one of the supported build regions.

   If you don't specify a config-file-path and source-directory in the gcloud builds submit command, Cloud Build assumes that the config file and the source code are in the current working directory.

   Once your build completes, you can view repository details in Artifact Registry.

   You can also view build provenance metadata and validate provenance.

Code examples

Here are some example repositories you can use to build Java apps, each of which contain a sample application and a build config file to build and test that application:

• maven-example: A Java app and an example build config file to build and test the app with mvn.
• gradle-example: A Java app and an example build config file to build and test the app with gradle.

What's next

• Learn how to view build results.
• Learn how to safeguard builds.
• Learn how to build standalone Java applications.
• Learn how to deploy an application on Cloud Run.
• Learn how to deploy an application on GKE.
• Learn how to troubleshoot build errors.