Setting up your Java project for Codespaces

Get started with your Java project in Codespaces by creating a custom dev container.

In this article

Note: Codespaces is currently in limited public beta and subject to change. For more information about joining the beta, see "About Codespaces."

Introduction

This guide shows you how to set up your Java project in Codespaces. It will take you through an example of opening your project in a codespace, and adding and modifying a dev container configuration from a template.

Prerequisites

  • You should have an existing Java project in a repository on GitHub.com. If you don't have a project, you can try this tutorial with the following example: https://github.com/microsoft/vscode-remote-try-java
  • You must have Codespaces enabled for your organization.

Step 1: Open your project in a codespace

  1. Navigate to your project's repository. Use the Code drop-down menu, and select Open with Codespaces. If you don’t see this option, your project isn’t available for Codespaces.

    Open with Codespaces button

  2. To create a new codespace, click New codespace. New codespace button

When you create a codespace, your project is created on a remote VM that is dedicated to you. By default, the container for your codespace has many languages and runtimes including Java, nvm, npm, and yarn. It also includes a common set of tools like git, wget, rsync, openssh, and nano.

You can customize your codespace by adjusting the amount of vCPUs and RAM, adding dotfiles to personalize your environment, or by modifying the tools and scripts installed.

Codespaces uses a file called devcontainer.json to store configurations. On launch Codespaces uses the file to install any tools, dependencies, or other set up that might be needed for the project. For more information, see "Configuring Codespaces for your project."

Step 2: Add a dev container to your codespace from a template

The default codespaces container comes with the latest Java version, package managers (Maven, Gradle), and other common tools preinstalled. However, we recommend that you set up a custom container to define the tools and scripts that your project needs. This will ensure a fully reproducible environment for all Codespaces users in your repository.

To set up your project with a custom container, you will need to use a devcontainer.json file to define the environment. In Codespaces you can add this either from a template or you can create your own. For more information on dev containers, see "Configuring Codespaces for your project."

  1. Access the Command Palette (Shift + Command + P / Ctrl + Shift + P), then start typing "dev container". Select Codespaces: Add Development Container Configuration Files....

    "Codespaces: Add Development Container Configuration Files..." in the command palette

  2. For this example, click Java. In practice, you could select any container that’s specific to Java or a combination of tools such as Java and Azure Functions. Select Java option from the list

  3. Click the recommended version of Java. Java version selection

  4. Access the command palette (Shift + Command + P/ Ctrl + Shift + P), then start typing "rebuild". Select Codespaces: Rebuild Container.

    Rebuild container option

Anatomy of your dev container

Adding the Java dev container template adds a .devcontainer folder to the root of your project's repository with the following files:

  • devcontainer.json
  • Dockerfile

The newly added devcontainer.json file defines a few properties that are described after the sample.

devcontainer.json

// For format details, see https://aka.ms/vscode-remote/devcontainer.json or this file's README at:
// https://github.com/microsoft/vscode-dev-containers/tree/v0.159.0/containers/java
{
    "name": "Java",
    "build": {
        "dockerfile": "Dockerfile",
        "args": {
            // Update the VARIANT arg to pick a Java version: 11, 14
            "VARIANT": "11",
            // Options
            "INSTALL_MAVEN": "true",
            "INSTALL_GRADLE": "false",
            "INSTALL_NODE": "false",
            "NODE_VERSION": "lts/*"
        }
    },

    // Set *default* container specific settings.json values on container create.
    "settings": { 
        "terminal.integrated.shell.linux": "/bin/bash",
        "java.home": "/docker-java-home",
        "maven.executable.path": "/usr/local/sdkman/candidates/maven/current/bin/mvn"
    },
    
    // Add the IDs of extensions you want installed when the container is created.
    "extensions": [
        "vscjava.vscode-java-pack"
    ],

    // Use 'forwardPorts' to make a list of ports inside the container available locally.
    // "forwardPorts": [],

    // Use 'postCreateCommand' to run commands after the container is created.
    // "postCreateCommand": "java -version",

    // Uncomment to connect as a non-root user. See https://aka.ms/vscode-remote/containers/non-root.
    "remoteUser": "vscode"
}
  • Name - You can name your dev container anything, this is just the default.
  • Build - The build properties.
    • Dockerfile - In the build object, dockerfile is a reference to the Dockerfile that was also added from the template.
    • Args
      • Variant: This file only contains one build argument, which is the Java version that is passed into the Dockerfile.
  • Settings - These are Visual Studio Code settings that you can set.
    • Terminal.integrated.shell.linux - While bash is the default here, you could use other terminal shells by modifying this.
  • Extensions - These are extensions included by default.
    • Vscjava.vscode-java-pack - The Java Extension Pack provides popular extensions for Java development to get you started.
  • forwardPorts - Any ports listed here will be forwarded automatically.
  • postCreateCommand - If you want to run anything after you land in your codespace that’s not defined in the Dockerfile, you can do that here.
  • remoteUser - By default, you’re running as the vscode user, but you can optionally set this to root.

Dockerfile

# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.159.0/containers/java/.devcontainer/base.Dockerfile
ARG VARIANT="14"
FROM mcr.microsoft.com/vscode/devcontainers/java:0-${VARIANT}

# [Optional] Install Maven or Gradle
ARG INSTALL_MAVEN="false"
ARG MAVEN_VERSION=3.6.3
ARG INSTALL_GRADLE="false"
ARG GRADLE_VERSION=5.4.1
RUN if [ "${INSTALL_MAVEN}" = "true" ]; then su vscode -c "source /usr/local/sdkman/bin/sdkman-init.sh && sdk install maven \"${MAVEN_VERSION}\""; fi \
    && if [ "${INSTALL_GRADLE}" = "true" ]; then su vscode -c "source /usr/local/sdkman/bin/sdkman-init.sh && sdk install gradle \"${GRADLE_VERSION}\""; fi

# [Optional] Install a version of Node.js using nvm for front end dev
ARG INSTALL_NODE="true"
ARG NODE_VERSION="lts/*"
RUN if [ "${INSTALL_NODE}" = "true" ]; then su vscode -c "source /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi

# [Optional] Uncomment this section to install additional OS packages.
# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
#     && apt-get -y install --no-install-recommends <your-package-list-here>

# [Optional] Uncomment this line to install global node packages.
# RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1

You can use the Dockerfile to add additional container layers to specify OS packages, Java versions, or global packages we want included in our Dockerfile.

Step 3: Modify your devcontainer.json file

With your dev container added and a basic understanding of what everything does, you can now make changes to configure it for your environment. In this example, you'll add properties to install extensions and your project dependencies when your codespace launches.

  1. In the Explorer, select the devcontainer.json file from the tree to open it. You might have to expand the .devcontainer folder to see it.

    "Codespaces: Rebuild Container" in the command palette

  2. Add the following lines to your devcontainer.json file after extensions.

    JSON
    "postCreateCommand": "npm install",
    "forwardPorts": [4000],

    For more information on devcontainer.json properties, see the devcontainer.json reference on the Visual Studio Code docs.

  3. Access the command palette (Shift + Command + P/ Ctrl + Shift + P), then start typing "rebuild". Select Codespaces: Rebuild Container.

    Rebuild container option

    Rebuilding inside your codespace ensures your changes work as expected before you commit the changes to the repository. If something does result in a failure, you’ll be placed in a codespace with a recovery container that you can rebuild from to keep adjusting your container.

Step 4: Run your application

In the previous section, you used the postCreateCommand to install a set of packages via npm. You can now use this to run our application with npm.

  1. Run your application by pressing F5.

  2. When your project starts, you should see a toast in the bottom right corner with a prompt to connect to the port your project uses.

    Port forwarding toast

Step 5: Commit your changes

Once you've made changes to your codespace, either new code or configuration changes, you'll want to commit your changes. Committing changes to your repository ensures that anyone else who creates a codespace from this repository has the same configuration. This also means that any customization you do, such as adding Visual Studio Code extensions, will appear for all users.

For information, see "Using source control in your codespace."

Next steps

You should now be ready start developing your Java project in Codespaces. Here are some additional resources for more advanced scenarios.

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