Spring Boot Docker Image: Introduction and Tutorial
Introduction
In today's software development landscape, containerization has become a popular approach for deploying applications. It allows developers to build, package, and ship applications along with their dependencies, ensuring consistency across different environments. Docker is one such containerization platform that provides a lightweight and portable runtime environment for applications. In this article, we will explore how to create a Docker image for a Spring Boot application.
Prerequisites
Before we dive into the steps, make sure you have the following prerequisites installed on your machine:
- Docker: You can download and install Docker from the official website (
- Java Development Kit (JDK): Ensure you have JDK 8 or later installed on your system
- Spring Boot: Familiarity with Spring Boot framework
Step 1: Create a Spring Boot Application
To demonstrate the process of creating a Docker image, let's start by creating a simple Spring Boot application. Open your favorite IDE and create a new Spring Boot project. You can use the Spring Initializr ( or Maven archetype to generate the project structure.
Once the project is created, you can add a simple REST controller to expose an API endpoint. Here is an example:
@RestController
public class GreetingController {
@GetMapping("/hello")
public String hello() {
return "Hello, Docker!";
}
}
Step 2: Build the Spring Boot Application
To build the Spring Boot application, open a terminal or command prompt and navigate to the root directory of your project. Use the following command to build the project:
./mvnw clean package
This will compile the code, run tests, and create an executable JAR file in the target directory.
Step 3: Write a Dockerfile
A Dockerfile is a text document that contains instructions for Docker on how to build a Docker image. Create a new file named Dockerfile in the root directory of your project and add the following content:
FROM openjdk:8-jdk-alpine
COPY target/myapp.jar myapp.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "myapp.jar"]
Let's break down the contents of the Dockerfile:
FROM openjdk:8-jdk-alpine: This line specifies the base image to use for the Docker image. In this case, we are using the official OpenJDK 8 Alpine image, which is a lightweight version of the JDK.COPY target/myapp.jar myapp.jar: This line copies the JAR file built in the previous step into the Docker image.EXPOSE 8080: This line exposes port 8080, which is the default port for Spring Boot applications.ENTRYPOINT ["java", "-jar", "myapp.jar"]: This line specifies the command to run when a container is started from the image. In this case, it runs the Java application using the executable JAR file.
Step 4: Build the Docker Image
To build the Docker image, navigate to the directory containing the Dockerfile in the terminal or command prompt. Use the following command:
docker build -t myapp .
This command builds the Docker image using the instructions defined in the Dockerfile and tags it with the name myapp.
Step 5: Run the Docker Container
Once the Docker image is built, you can run a Docker container based on that image. Use the following command:
docker run -p 8080:8080 myapp
This command starts a Docker container based on the myapp image and maps port 8080 of the container to port 8080 of the host machine.
Conclusion
In this tutorial, we have learned how to create a Docker image for a Spring Boot application. We started by creating a simple Spring Boot application and then built a Docker image using a Dockerfile. Finally, we ran a Docker container based on the image. Containerization with Docker provides several benefits, such as isolation, portability, and scalability, making it an ideal choice for deploying Spring Boot applications.
