Create an image of a Java app’s .jar file and then use that image to launch a Docker container.

First you need to have a .jar file in a directory

In the same directory, you create a file:

Dockerfile

with content:

# Usamos una imagen de Java 21 ligera
FROM eclipse-temurin:21-jdk-alpine

# Directorio de trabajo dentro del contenedor
WORKDIR /app

# Copiamos el jar generado (asegúrate de que el nombre coincida)
COPY ./*.jar app.jar

# Exponemos el puerto de Spring Boot
EXPOSE 8080

# Comando para arrancar la app
ENTRYPOINT ["java", "-jar", "app.jar"]

8080 is the port of the java app springboot gradle

If we are in the same directory as the .jar file, we create the image for Docker:

docker build -t mi-app-custom .

• The image is not created in the same directory as the .jar file
• Docker stores the images internally and you can view them with “docker images”

We can see the Docker images we have, with the command:

docker images

The images should include the image of the Java app creator “mi-app-custom”

Then we need to create a container with that image

docker run -d -p 8090:8090 --name mi-contenedor-spring mi-app-custom

A mapping is done between the output port of the app .jar and the port of localhost (which is the container)

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if you want delete the image:

docker rmi -f mi-app-custom

if you want see the container (until the off):

docker ps -a

the starters:

docker ps