Last Updated on January 11, 2020

With Docker, we can create portable Java CLI applications for various environments by pre-building container images. This could make deployment a lot easier and less messy in particularly in Production environments. This post briefly demonstrates how to create a Docker image with a Java CLI application.

Requirements

We used the following for this post.

Docker for Windows (Docker Desktop Community)
OpenJDK 8
SpringBoot
Maven

The CLI Application

The application is a Spring Boot application generated via Spring Initializr in IntelliJ IDEA. It has this simple main class:

package com.turreta.cli.docker.comturretaclidocker;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.util.concurrent.TimeUnit;

@SpringBootApplication
public class ComTurretaCliDockerApplication
{
    public static void main(String[] args) throws InterruptedException
    {
        SpringApplication.run(ComTurretaCliDockerApplication.class, args);
        System.out.println("######################################");
        System.out.println("In Java CLI App in a Docker container");
        System.out.println("######################################");
        TimeUnit.SECONDS.sleep(30);
    }
}

package com.turreta.cli.docker.comturretaclidocker;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.util.concurrent.TimeUnit;

@SpringBootApplication

public class ComTurretaCliDockerApplication

{

public static void main(String[] args) throws InterruptedException

{

SpringApplication.run(ComTurretaCliDockerApplication.class, args);

System.out.println("######################################");

System.out.println("In Java CLI App in a Docker container");

System.out.println("######################################");

TimeUnit.SECONDS.sleep(30);

}

Nothing fancy.

pom.xml

The pom.xml file has these information:

...
    <groupId>com.turreta.cli.docker</groupId>
    <artifactId>com-turreta-cli-docker</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>com-turreta-cli-docker</name>
...

...

<groupId>com.turreta.cli.docker</groupId>

<artifactId>com-turreta-cli-docker</artifactId>

<version>0.0.1-SNAPSHOT</version>

<name>com-turreta-cli-docker</name>

...

DockerFile

We need a DockerFile file. Create it in the same project directory. It is used to build our desired Docker image locally.

# Pull base image.
FROM openjdk:8

LABEL maintainer="www.turreta.com"

RUN mkdir /app
	
ARG JAR_FILE 

ENV JAVA_XMS=512 JAVA_XMX=1024

COPY /target/${JAR_FILE}.jar /app/app.jar

WORKDIR /app
ENTRYPOINT java -Xms${JAVA_XMS}m -Xmx${JAVA_XMX}m \
    -Djava.security.egd=file:/dev/./urandom -jar app.jar

# Pull base image.

FROM openjdk:8

LABEL maintainer="www.turreta.com"

RUN mkdir /app

ARG JAR_FILE

ENV JAVA_XMS=512 JAVA_XMX=1024

COPY /target/${JAR_FILE}.jar /app/app.jar

WORKDIR /app

ENTRYPOINT java -Xms${JAVA_XMS}m -Xmx${JAVA_XMX}m \

-Djava.security.egd=file:/dev/./urandom -jar app.jar

Build, Run to Test

Build Project

First we need to build our Maven project using the following command to create the jar file in the target directory.

clean package

1	clean package

Build Docker Image

Next, we invoke the following command in command-prompt in the same directory where the DockerFile is. Note that we specified the artifactId and version. The file name of the generated jar file is also used here.

docker build -t turreta.com/cli-docker:0.0.1-SNAPSHOT --build-arg JAR_FILE=com-turreta-cli-docker-0.0.1-SNAPSHOT .

1	docker build -t turreta.com/cli-docker:0.0.1-SNAPSHOT --build-arg JAR_FILE=com-turreta-cli-docker-0.0.1-SNAPSHOT .

We will then get the following console output:

build-arg JAR_FILE=com-turreta-cli-docker-0.0.1-SNAPSHOT .
Sending build context to Docker daemon  7.742MB                                                                         
Step 1/8 : FROM openjdk:8
 ---> 27da2af61908
Step 2/8 : LABEL maintainer="www.turreta.com"
 ---> Running in 3b4301a1033c
Removing intermediate container 3b4301a1033c
 ---> dcb5f766bfa6
Step 3/8 : RUN  mkdir /app
 ---> Running in 39dc6d724012
Removing intermediate container 39dc6d724012
 ---> 209ab82f3a87
Step 4/8 : ARG JAR_FILE
 ---> Running in ae2cd6744a1f
Removing intermediate container ae2cd6744a1f
 ---> d7e6b4574348
Step 5/8 : ENV JAVA_XMS=512 JAVA_XMX=1024
 ---> Running in cdb1a009e38b
Removing intermediate container cdb1a009e38b
 ---> db7156ee44b5
Step 6/8 : COPY /target/${JAR_FILE}.jar /app/app.jar
 ---> c5fc31c99f98
Step 7/8 : WORKDIR /app
 ---> Running in a388e2b5a010
Removing intermediate container a388e2b5a010
 ---> 94c0e98e72a2
Step 8/8 : ENTRYPOINT java -Xms${JAVA_XMS}m -Xmx${JAVA_XMX}m     -Djava.security.egd=file:/dev/./urandom -jar app.jar
 ---> Running in 8d362c78c7e1
Removing intermediate container 8d362c78c7e1
 ---> 075f8831395c
Successfully built 075f8831395c                                                                                         
Successfully tagged turreta.com/cli-docker:0.0.1-SNAPSHOT                                                               
SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host. All files and directories added to build 
context will have '-rwxr-xr-x' permissions. It is recommended to double check and reset permissions for sensitive files and directories.

build-arg JAR_FILE=com-turreta-cli-docker-0.0.1-SNAPSHOT .

Sending build context to Docker daemon 7.742MB

Step 1/8 : FROM openjdk:8

---> 27da2af61908

Step 2/8 : LABEL maintainer="www.turreta.com"

---> Running in 3b4301a1033c

Removing intermediate container 3b4301a1033c

---> dcb5f766bfa6

Step 3/8 : RUN mkdir /app

---> Running in 39dc6d724012

Removing intermediate container 39dc6d724012

---> 209ab82f3a87

Step 4/8 : ARG JAR_FILE

---> Running in ae2cd6744a1f

Removing intermediate container ae2cd6744a1f

---> d7e6b4574348

Step 5/8 : ENV JAVA_XMS=512 JAVA_XMX=1024

---> Running in cdb1a009e38b

Removing intermediate container cdb1a009e38b

---> db7156ee44b5

Step 6/8 : COPY /target/${JAR_FILE}.jar /app/app.jar

---> c5fc31c99f98

Step 7/8 : WORKDIR /app

---> Running in a388e2b5a010

Removing intermediate container a388e2b5a010

---> 94c0e98e72a2

Step 8/8 : ENTRYPOINT java -Xms${JAVA_XMS}m -Xmx${JAVA_XMX}m -Djava.security.egd=file:/dev/./urandom -jar app.jar

---> Running in 8d362c78c7e1

Removing intermediate container 8d362c78c7e1

---> 075f8831395c

Successfully built 075f8831395c

Successfully tagged turreta.com/cli-docker:0.0.1-SNAPSHOT

SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host. All files and directories added to build

context will have '-rwxr-xr-x' permissions. It is recommended to double check and reset permissions for sensitive files and directories.

Run the Application

Now we can ran our application using the following command.

docker run --rm turreta.com/cli-docker:0.0.1-SNAPSHOT

1	docker run --rm turreta.com/cli-docker:0.0.1-SNAPSHOT

The --rm option is to automatically clean up the container and remove the file system when the container exits. Please see https://docs.docker.com/engine/reference/run/.