How to Build Java Application with Docker

Docker has revolutionized the way applications are built and deployed. With its powerful containerization technology, Docker allows developers to package their applications along with all the necessary dependencies and configurations, and deploy them in a consistent and repeatable manner. In this article, we will explore how to build a Java application with Docker.

Prerequisites:

Before we begin, make sure you have the following prerequisites installed on your system:

• Docker
• Java Development Kit (JDK)

Step 1: Create a Simple Java Application

Let's create a simple Java application to demonstrate how to build it with Docker. Open your favorite text editor and create a new file named "HelloWorld.java". Copy and paste the following code into the file:

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

Save the file and close the editor.

Step 2: Compile the Java Application

Compile the Java application by running the following command in the terminal:

javac HelloWorld.java

This will generate a file named "HelloWorld.class" in the same directory.

Step 3: Create a Dockerfile

Now, create a Dockerfile in the same directory as the Java application. A Dockerfile is a script that contains instructions for building a Docker image. Copy and paste the following code into the Dockerfile:

FROM openjdk:11
COPY . /usr/src/myapp
WORKDIR /usr/src/myapp
RUN javac HelloWorld.java
CMD ["java", "HelloWorld"]

This Dockerfile instructs Docker to use the official OpenJDK 11 image as the base image, copy the Java application to the "/usr/src/myapp" directory inside the container, compile the Java application, and then run the "java HelloWorld" command when the container starts.

Step 4: Build the Docker Image

Build the Docker image by running the following command in the terminal:

docker build -t my-java-app .

This command tells Docker to build a Docker image with the tag "my-java-app" using the Dockerfile in the current directory (denoted by the "." symbol).

Step 5: Run the Docker Container

Run the Docker container by running the following command in the terminal:

docker run my-java-app

This command tells Docker to start a container from the "my-java-app" image.

You should see the following output in the terminal:

Hello, World!

Congratulations! You have successfully built a Java application with Docker.

More Examples:

If you want to try building a more complex Java application with Docker, you can follow the same steps as above but with a different Java application. Here are a few examples:

• Spring Boot Application: Create a Spring Boot application and follow the same steps as above to build it with Docker. Make sure to use the appropriate base image and add any necessary dependencies to the Dockerfile.
• Multi-Module Maven Project: If your Java application is a multi-module Maven project, you can use the Maven Docker Plugin to build the Docker image. This plugin automatically generates a Dockerfile based on the Maven project structure and builds the Docker image using the Dockerfile.

In this article, we have learned how to build a Java application with Docker. By following the steps outlined in this article, you can easily package your Java application into a Docker image and deploy it in a consistent and repeatable manner.

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That's it for this post. Keep practicing and have fun. Leave your comments if any.