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Play with Docker and Java

ยท 4 min read

Play with Docker and Java

In this post, we'll play with Docker and Java. Since there are ready-to-use Java images for Docker you don't need to install or configure anything other than Docker.

I don't know Java at all

You just need to know, I've absolutely no skills in Java. Which software should be installed, how to run a script and so on. I'll just rely on a very few Docker commands and, about the installation, yeah, using Docker, it's easy: nothing to install, nothing to configure.

Please start a Linux shell and run mkdir -p /tmp/java && cd $_ to create a folder called java in your Linux temporary folder and jump in it.

Please create a new file called with this content:

public class Main
public static void main(String[] args) {
System.out.println("Hello, World");

Now, you'll need to compile your source. For this, just run docker run -it --rm -v ${PWD}:/app -w /app -u 1000:1000 openjdk:11 javac

Docker CLI reminder

As a reminder, the used Docker run command are (almost always the same):

  • -it to start Docker interactively, this will allow the script running in the container to ask you for some prompts f.i.,
  • --rm to ask Docker to kill and remove the container as soon as the script has been executed (otherwise you'll have a lot of exited but not removed Docker containers; you can check this by not using the --rm flag then running docker container list on the console),
  • -v ${PWD}:/app to share your current folder with a folder called /app in the Docker container,
  • -w /app to tell Docker that the current directory, in the container, will be the /app folder,
  • -u 1000:1000 ask Docker to reuse our local credentials so when a file is updated/created in the container, the file will be owned by us,
  • then openjdk:11 which is the name and the version of the Docker image to use, and, finally,
  • javac i.e. the command line to start within the container.

As a result of this command, your source will be compiled into the Main.class file.

By running ls -alh you can verify that, yes, the java script has been compiled into a .java file.

โฏ ls -alh

total 24K
drwxr-xr-x 2 christophe christophe 4.0K Nov 22 15:02 .
drwxrwxrwt 29 root root 12K Nov 22 14:58 ..
-rw-r--r-- 1 christophe christophe 414 Nov 22 15:02 Main.class
-rw-r--r-- 1 christophe christophe 117 Nov 22 14:58
And without to have to install something

Once again, you don't have install or configure something; just call the Docker image that goes well.

Last thing is to execute your Java program. Now, please run docker run --rm -v $PWD:/app -w /app openjdk:11 java Main to execute it.

โฏ docker run --rm -v $PWD:/app -w /app openjdk:11 java Main

Hello, World

A little more difficult, calling a REST APIโ€‹

Please create a new file called with this content:

package restclient;

public class API {
public static void main(String[] args) {
try {
URL url = new URL("");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestProperty("Accept", "application/json");

if (conn.getResponseCode() != 200) {
throw new RuntimeException("Failed : HTTP Error code : "
+ conn.getResponseCode());

InputStreamReader in = new InputStreamReader(conn.getInputStream());
BufferedReader br = new BufferedReader(in);
String output;

while ((output = br.readLine()) != null) {


} catch (Exception e) {
System.out.println("Exception in NetClientGet:- " + e);

Compile it by running docker run --rm -v $PWD:/app -w /app -u 1000:1000 openjdk:11 javac; get the API.class file.

Finally, call docker run --rm -v $PWD:/app -w /app openjdk:11 java to execute the API call and display the result on screen:

โฏ docker run --rm -v $PWD:/app -w /app openjdk:11 java
"userId": 1,
"id": 1,
"title": "delectus aut autem",
"completed": false

This example will use the sample to generate one fake TODO. The JSON will be displayed on the command line.

You're ready to start your Java's coding journey. Have fun.