This project demonstrates the difference between ENTRYPOINT and CMD in a Dockerfile using a minimal java web application built with Maven. The application displays a simple web page. Its appearance and text change based on whether a --special flag is passed as an argument when running the Docker container.

• pom.xml: Maven project configuration.
• src/: Java source code for the Spring Boot application.
• Dockerfile: Instructions to build the Docker image (builds the app inside).

1. Navigate to the project's root directory (where the Dockerfile is located) in your terminal.
2. Run the Docker build command:

docker build -t java-app .

(You can replace java-app with any image name you prefer)

This command reads the Dockerfile, downloads the base Maven image, copies the project files, builds the Java application using mvn package inside the container, and creates the final image.

The Dockerfile uses ENTRYPOINT to set the base command (java -jar /app/target/demo-0.0.1-SNAPSHOT.jar) and CMD to provide default arguments (none in this case). Arguments provided after the image name in docker run override the CMD and are appended to the ENTRYPOINT.

To run the container without any extra arguments,

docker run -d -p 8080:8080 --name demo-default java-app

• -d: Run in detached (background) mode.
• -p 8080:8080: Map port 8080 on your host to port 8080 in the container.
• --name demo-default: Assign a name to the container for easy management.

Expected Output: Open your web browser to http://<ip-address>:8080. You should see the web page styled for the DEFAULT mode (e.g., orange theme).

To run the container and activate the special behavior, pass the --special flag after the image name. This flag overrides the default CMD and is appended to the ENTRYPOINT command.

docker run -d -p 8080:8080 --name demo-special java-app --special

The command executed inside the container becomes effectively: java -jar /app/target/demo-0.0.1-SNAPSHOT.jar --special

Expected Output: Open your web browser to http://<ip-address>:8080. You should see the web page styled for the SPECIAL mode (e.g., cyan theme).

This demonstrates how ENTRYPOINT provides the fixed executable part of the command, while arguments passed to docker run (which override CMD) allow you to modify the behavior of that executable.