Docker - Creating simple java image

This is my "Hello World" of creating my own docker image for running a Java program in Java 7 environment.

You can find information about Docker here. Developers need to understand concepts like Docker, docker-machine and how to write a Dockerfile to be able to create own docker images.

Create Dockerfile 

This is how a Dockerfile for our project would look like:

FROM java:7

MAINTAINER tuhin.gupta@gmail.com

COPY ./src/main/java /usr/src/myjavaapp

WORKDIR /usr/src/myjavaapp

RUN javac com/tuhin/example/Main.java 

CMD ["java", "com.tuhin.example.Main"]

see details of Dockerfile syntax here

In our project we are using following instructions:

FROM - tell docker to pull java 7 image

MAINTAINER - instruction allows to set the author field

COPY - instruction is to copy the java source code to docker image file system

WORKDIR - sets the work directory in docker image

RUN - runs javac at the specified location

CMD - this instruction can run any command that can be run from command prompt.

Java code in Main.java is:

package com.tuhin.example;

/**

 * @author Tuhin Gupta

 *

 */

public class Main {

public static void main(String[] args) {

System.out.println("This is the main class.");

}

}

Build Docker Image

Once the Dockerfile is created, now we need to build the docker image for java application

$ docker build -f <path-to-docker-context>/docker/Dockerfile -t myjavaapp <path-to-docker-context>

Above command will build the docker image.

-f : is used to specify the path to docker file within docker context. Dockerfile must be in docker context.

-t : Repository name (and optionally a tag) for the image

This command will build the docker image and you can view your recently created image using following command:

$ docker images

REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE

myjavaapp                 latest              45a3aacd5bd0          1 hours ago                590.1 MB

Run your Docker Image

To run the newly created image and the java program inside the image, use following command:

$ docker run -t --rm --name test-myjavaapp myjavaapp 

This will run myjavaapp image and Main.java class within it.

Save your Docker Image as tar file for sharing

Using following command, you can save a docker image as tar file and share between developers.

$ docker save -o <path-to-save>/myjavaapp.tar <image id>

<image id>: image id from docker images command

Refer to my Github site - https://github.com/tuhingupta/docker-simple-java and download the Dockerfile.