---
title: Containerize a Java application
linkTitle: Containerize your app
weight: 10
keywords: java, containerize, initialize, maven, build
description: Learn how to containerize a Java application.
aliases:
  - /language/java/build-images/
  - /language/java/run-containers/
  - /language/java/containerize/
  - /guides/language/java/containerize/
---

## Prerequisites

- You have installed the latest version of [Docker Desktop](/get-started/get-docker.md).
  Docker adds new features regularly and some parts of this guide may
  work only with the latest version of Docker Desktop.

* You have a [Git client](https://git-scm.com/downloads). The examples in this
  section use a command-line based Git client, but you can use any client.

## Overview

This section walks you through containerizing and running a Java
application.

## Get the sample applications

Clone the sample application that you'll be using to your local development machine. Run the following command in a terminal to clone the repository.

```console
$ git clone https://github.com/spring-projects/spring-petclinic.git
```

The sample application is a Spring Boot application built using Maven. For more details, see `readme.md` in the repository.

## Initialize Docker assets

Now that you have an application, you can create the necessary Docker assets to
containerize your application. You can use Docker Desktop's built-in Docker Init
feature to help streamline the process, or you can manually create the assets.

{{< tabs >}}
{{< tab name="Use Docker Init" >}}

Inside the `spring-petclinic` directory, run the `docker init` command. `docker
init` provides some default configuration, but you'll need to answer a few
questions about your application. Refer to the following example to answer the
prompts from `docker init` and use the same answers for your prompts.

The sample application already contains Docker assets. You'll be prompted to overwrite the existing Docker assets. To continue with this guide, select `y` to overwrite them.

```console
$ docker init
Welcome to the Docker Init CLI!

This utility will walk you through creating the following files with sensible defaults for your project:
  - .dockerignore
  - Dockerfile
  - compose.yaml
  - README.Docker.md

Let's get started!

WARNING: The following Docker files already exist in this directory:
  - docker-compose.yml
? Do you want to overwrite them? Yes
? What application platform does your project use? Java
? What's the relative directory (with a leading .) for your app? ./src
? What version of Java do you want to use? 21
? What port does your server listen on? 8080
```

In the previous example, notice the `WARNING`. `docker-compose.yaml` already
exists, so `docker init` overwrites that file rather than creating a new
`compose.yaml` file. This prevents having multiple Compose files in the
directory. Both names are supported, but Compose prefers the canonical
`compose.yaml`.

{{< /tab >}}
{{< tab name="Manually create assets" >}}

If you don't have Docker Desktop installed or prefer creating the assets
manually, you can create the following files in your project directory.

Create a file named `Dockerfile` with the following contents.

```dockerfile {collapse=true,title=Dockerfile}
# syntax=docker/dockerfile:1

# Comments are provided throughout this file to help you get started.
# If you need more help, visit the Dockerfile reference guide at
# https://docs.docker.com/go/dockerfile-reference/

# Want to help us make this template better? Share your feedback here: https://forms.gle/ybq9Krt8jtBL3iCk7

################################################################################

# Create a stage for resolving and downloading dependencies.
FROM eclipse-temurin:21-jdk-jammy as deps

WORKDIR /build

# Copy the mvnw wrapper with executable permissions.
COPY --chmod=0755 mvnw mvnw
COPY .mvn/ .mvn/

# Download dependencies as a separate step to take advantage of Docker's caching.
# Leverage a cache mount to /root/.m2 so that subsequent builds don't have to
# re-download packages.
RUN --mount=type=bind,source=pom.xml,target=pom.xml \
    --mount=type=cache,target=/root/.m2 ./mvnw dependency:go-offline -DskipTests

################################################################################

# Create a stage for building the application based on the stage with downloaded dependencies.
# This Dockerfile is optimized for Java applications that output an uber jar, which includes
# all the dependencies needed to run your app inside a JVM. If your app doesn't output an uber
# jar and instead relies on an application server like Apache Tomcat, you'll need to update this
# stage with the correct filename of your package and update the base image of the "final" stage
# use the relevant app server, e.g., using tomcat (https://hub.docker.com/_/tomcat/) as a base image.
FROM deps as package

WORKDIR /build

COPY ./src src/
RUN --mount=type=bind,source=pom.xml,target=pom.xml \
    --mount=type=cache,target=/root/.m2 \
    ./mvnw package -DskipTests && \
    mv target/$(./mvnw help:evaluate -Dexpression=project.artifactId -q -DforceStdout)-$(./mvnw help:evaluate -Dexpression=project.version -q -DforceStdout).jar target/app.jar

################################################################################

# Create a stage for extracting the application into separate layers.
# Take advantage of Spring Boot's layer tools and Docker's caching by extracting
# the packaged application into separate layers that can be copied into the final stage.
# See Spring's docs for reference:
# https://docs.spring.io/spring-boot/docs/current/reference/html/container-images.html
FROM package as extract

WORKDIR /build

RUN java -Djarmode=layertools -jar target/app.jar extract --destination target/extracted

################################################################################

# Create a new stage for running the application that contains the minimal
# runtime dependencies for the application. This often uses a different base
# image from the install or build stage where the necessary files are copied
# from the install stage.
#
# The example below uses eclipse-turmin's JRE image as the foundation for running the app.
# By specifying the "17-jre-jammy" tag, it will also use whatever happens to be the
# most recent version of that tag when you build your Dockerfile.
# If reproducibility is important, consider using a specific digest SHA, like
# eclipse-temurin@sha256:99cede493dfd88720b610eb8077c8688d3cca50003d76d1d539b0efc8cca72b4.
FROM eclipse-temurin:21-jre-jammy AS final

# Create a non-privileged user that the app will run under.
# See https://docs.docker.com/go/dockerfile-user-best-practices/
ARG UID=10001
RUN adduser \
    --disabled-password \
    --gecos "" \
    --home "/nonexistent" \
    --shell "/sbin/nologin" \
    --no-create-home \
    --uid "${UID}" \
    appuser
USER appuser

# Copy the executable from the "package" stage.
COPY --from=extract build/target/extracted/dependencies/ ./
COPY --from=extract build/target/extracted/spring-boot-loader/ ./
COPY --from=extract build/target/extracted/snapshot-dependencies/ ./
COPY --from=extract build/target/extracted/application/ ./

EXPOSE 8080

ENTRYPOINT [ "java", "org.springframework.boot.loader.launch.JarLauncher" ]
```

The sample already contains a Compose file. Overwrite this file to follow along with the guide. Update the`docker-compose.yaml` with the following contents.

```yaml {collapse=true,title=docker-compose.yaml}
# Comments are provided throughout this file to help you get started.
# If you need more help, visit the Docker Compose reference guide at
# https://docs.docker.com/go/compose-spec-reference/

# Here the instructions define your application as a service called "server".
# This service is built from the Dockerfile in the current directory.
# You can add other services your application may depend on here, such as a
# database or a cache. For examples, see the Awesome Compose repository:
# https://github.com/docker/awesome-compose
services:
  server:
    build:
      context: .
    ports:
      - 8080:8080
# The commented out section below is an example of how to define a PostgreSQL
# database that your application can use. `depends_on` tells Docker Compose to
# start the database before your application. The `db-data` volume persists the
# database data between container restarts. The `db-password` secret is used
# to set the database password. You must create `db/password.txt` and add
# a password of your choosing to it before running `docker compose up`.
#     depends_on:
#       db:
#         condition: service_healthy
#   db:
#     image: postgres:18
#     restart: always
#     user: postgres
#     secrets:
#       - db-password
#     volumes:
#       - db-data:/var/lib/postgresql
#     environment:
#       - POSTGRES_DB=example
#       - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
#     expose:
#       - 5432
#     healthcheck:
#       test: [ "CMD", "pg_isready" ]
#       interval: 10s
#       timeout: 5s
#       retries: 5
# volumes:
#   db-data:
# secrets:
#   db-password:
#     file: db/password.txt

```

Create a file named `.dockerignore` with the following contents.

```text {collapse=true,title=".dockerignore"}
# Include any files or directories that you don't want to be copied to your
# container here (e.g., local build artifacts, temporary files, etc.).
#
# For more help, visit the .dockerignore file reference guide at
# https://docs.docker.com/go/build-context-dockerignore/

**/.classpath
**/.dockerignore
**/.env
**/.git
**/.gitignore
**/.project
**/.settings
**/.toolstarget
**/.vs
**/.vscode
**/.next
**/.cache
**/*.*proj.user
**/*.dbmdl
**/*.jfm
**/charts
**/docker-compose*
**/compose.y*ml
**/target
**/Dockerfile*
**/node_modules
**/npm-debug.log
**/obj
**/secrets.dev.yaml
**/values.dev.yaml
**/vendor
LICENSE
README.md
```

{{< /tab >}}
{{< /tabs >}}

You should now have the following three files in your `spring-petclinic`
directory.

- [Dockerfile](/reference/dockerfile/)
- [.dockerignore](/reference/dockerfile/#dockerignore-file)
- [docker-compose.yaml](/reference/compose-file/_index.md)

## Run the application

Inside the `spring-petclinic` directory, run the following command in a
terminal.

```console
$ docker compose up --build
```

The first time you build and run the app, Docker downloads dependencies and builds the app. It may take several minutes depending on your network connection.

Open a browser and view the application at [http://localhost:8080](http://localhost:8080). You should see a simple app for a pet clinic.

In the terminal, press `ctrl`+`c` to stop the application.

### Run the application in the background

You can run the application detached from the terminal by adding the `-d`
option. Inside the `spring-petclinic` directory, run the following command
in a terminal.

```console
$ docker compose up --build -d
```

Open a browser and view the application at [http://localhost:8080](http://localhost:8080). You should see a simple app for a pet clinic.

In the terminal, run the following command to stop the application.

```console
$ docker compose down
```

For more information about Compose commands, see the
[Compose CLI reference](/reference/cli/docker/compose/).

## Summary

In this section, you learned how you can containerize and run a Java
application using Docker.

Related information:

- [docker init reference](/reference/cli/docker/init/)

## Next steps

In the next section, you'll learn how you can develop your application using
Docker containers.
