How to build a docker container for a Java application

The docker registry hub has a Maven image that can be used to create java containers.

Using this approach the build machine does not need to have either Java or Maven pre-installed, Docker controls the entire build process.

Example

├── Dockerfile
├── pom.xml
└── src
    ├── main
    │   ├── java
    │   │   └── org
    │   │       └── demo
    │   │           └── App.java
    │   └── resources
    │       └── log4j.properties
    └── test
        └── java
            └── org
                └── demo
                    └── AppTest.java

Image is built as follows:

docker build -t my-maven .

And run as follows:

$ docker run -it --rm my-maven
0    [main] INFO  org.demo.App  - hello world

Dockerfile

FROM maven:3.3-jdk-8-onbuild
CMD ["java","-jar","/usr/src/app/target/demo-1.0-SNAPSHOT-jar-with-dependencies.jar"]

---

Update

If you wanted to optimize your image to exclude the source you could create a Dockerfile that only includes the built jar:

FROM java:8
ADD target/demo-1.0-SNAPSHOT-jar-with-dependencies.jar /opt/demo/demo-1.0-SNAPSHOT-jar-with-dependencies.jar
CMD ["java","-jar","/opt/demo/demo-1.0-SNAPSHOT-jar-with-dependencies.jar"]

And build the image in two steps:

docker run -it --rm -w /opt/maven \
   -v $PWD:/opt/maven \
   -v $HOME/.m2:/root/.m2 \
   maven:3.3-jdk-8 \
   mvn clean install

docker build -t my-app .

__

Update (2017-07-27)

Docker now has a multi-stage build capability. This enables Docker to build an image containing the build tools but only the runtime dependencies.

The following example demonstrates this concept, note how the jar is copied from target directory of the first build phase

FROM maven:3.3-jdk-8-onbuild 

FROM java:8
COPY --from=0 /usr/src/app/target/demo-1.0-SNAPSHOT.jar /opt/demo.jar
CMD ["java","-jar","/opt/demo.jar"]

The easiest way is to let the build tool control the process. Otherwise, you would have to maintain your build tool's build file (like pom.xml for Maven or build.gradle for Gradle) as well as a Dockerfile.

A simple way to build a Docker container for your Java app is to use Jib, which is available as Maven and Gradle plugins.

For example, if you are using Maven and want to build your container to your running Docker daemon, you can just run this one command:

mvn compile com.google.cloud.tools:jib-maven-plugin:0.9.2:dockerBuild

You can also build directly to a Docker registry with Jib without needing to install docker, run a Docker daemon (which requires root privileges), or write a Dockerfile. It's also faster and builds images reproducibly.

See more about Jib at its Github repo: https://github.com/GoogleContainerTools/jib

Structure of java aplication

Demo
└── src
|    ├── main
|    │   ├── java
|    │   │   └── org
|    │   │       └── demo
|    │   │           └── App.java
|    │   └── resources
|    │       └── application.properties
|    └── test
|         └── java
|               └── org
|                   └── demo
|                         └── App.java  
├──── Dockerfile
├──── pom.xml

Content of Dockerfile

FROM java:8
EXPOSE 8080
ADD /target/demo.jar demo.jar
ENTRYPOINT ["java","-jar","demo.jar"]

Commands to build and run image

• Go to the directory of project.Lets say D:/Demo

$ cd D/demo
$ mvn clean install
$ docker build demo .
$ docker run -p 8080:8080 -t demo

Check that container is running or not

$ docker ps

The output will be

CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                    NAMES
55c11a464f5a        demo1               "java -jar demo.jar"   21 seconds ago      Up About a minute   0.0.0.0:8080->8080/tcp   cranky_mayer