AKR Developer Blog | Inject maven dependencies into Docker image

1. Story

As a Java developer I want to build a Docker image
I want to aquire a Docker feature named multi-stage builds
While that process I want to prevent downloading mvn dependecies through building docker image process
So I want to manually inject dependencies into Docker image

2. Build Docker image

1. Sample project:

As a simple sample project we have a Spring-Boot hello world project which responses on http://localhost:8080 You can provide your desired project or clone/download the github repository from here: https://github.com/AmirKeshavarz/hello-docker-java

1. Create local Maven repo:

In terminal go to the project directory and run below command to download all maven dependencies and put them in a compressed file:

    # mvn dependency:go-offline -Dmaven.repo.local=./repo package
    # tar cf repo.tar.gz ./repo

1 2	# mvn dependency:go-offline -Dmaven.repo.local=./repo package # tar cf repo.tar.gz ./repo

* dependecy:go-offline cause all dependencies being downloaded * -Dmaven.repo.local=./repo makes a directory named repo and download all dependencies into it

1. Create Dockerfile:

In project directory create a file named Dockerfile-injectrepo(Or it exists if you clone from our github)

# Step : build and package
FROM maven:3.6-openjdk-17-slim as BUILD
ADD repo.tar.gz /usr/share/maven/ref/
COPY . /usr/src/app
WORKDIR /usr/src/app
RUN mvn dependency:go-offline package

# Step : final docker image
FROM openjdk:17-jdk-alpine
EXPOSE 8080
COPY --from=BUILD /usr/src/app/target /opt/target
WORKDIR /opt/target
CMD ["java", "jar", "hello.jar"]

# Step : build and package

FROM maven:3.6-openjdk-17-slim as BUILD

ADD repo.tar.gz /usr/share/maven/ref/

COPY . /usr/src/app

WORKDIR /usr/src/app

RUN mvn dependency:go-offline package

# Step : final docker image

FROM openjdk:17-jdk-alpine

EXPOSE 8080

COPY --from=BUILD /usr/src/app/target /opt/target

WORKDIR /opt/target

CMD ["java", "jar", "hello.jar"]

Note that in line 3 ADD command is injecting our pre downloaded maven repo into first stage of our Docker image.

1. Build docker image:

For this step Docker must be installed on your system In terminal go to root of the project and run below command for building docker image:

# docker build -f Dockerfile-injectrepo -t mytutorial/hello .

1	# docker build -f Dockerfile-injectrepo -t mytutorial/hello .

* Please notice that there is a dot(.) at the end of above command. In terminal run below command for having a test and run the container:

# docker run mytutorial/hello -p 8080:8080

1	# docker run mytutorial/hello -p 8080:8080

Go to browser and browse into http:\localhost:8080

Below, a couple of points are mentioned which are not described here to keep this article simple.

Use -v option of docker for mounting your local maven repository and prevent downloading maven dependencies in build repetitive phase.
Use Maven plugins for building images instead of direct docker CLI commands.
Push docker image into a docker hub to make it accessible from hosts outer of your local.

Inject maven dependencies into Docker image
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2. Build Docker image

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