Docker

Build your Java image

To complete this tutorial, you need the following:

• Docker running locally.

• A Git client

• text editor to edit files.

1. Clone and run a Spring Boot application with Maven:-

Let’s clone the sample application that we'll be using in this module to our local development machine 

cd  /java_projects

git clone https://gitlab.com/javax2/user-service.git

cd user-service

Test the application without Docker

mvnw spring-boot:run 

To test that the application is working properly, open a new browser and navigate to

 http://localhost:8080/users/abc

 Press CTRL-c from within the terminal session where the server is running to stop it. 

2. Create a new Dockerfile which contains instructions required to build a Java image

# syntax=docker/dockerfile:1

FROM eclipse-temurin:17-jdk-jammy

WORKDIR /app

COPY .mvn/ .mvn

COPY mvnw pom.xml ./

RUN ./mvnw dependency:resolve

COPY src ./src

CMD ["./mvnw", "spring-boot:run"]

New Docker file

# syntax=docker/dockerfile:1

FROM maven:3.8.3-openjdk-17

WORKDIR /usr/src/app

COPY . /usr/src/app

RUN mvn package

#ENV PORT 5000

#EXPOSE $PORT

CMD [ "sh", "-c", "mvn -Dserver.port=${PORT} spring-boot:run" ]

Create a .dockerignore file (Optional)

To increase the performance of the build, and as a general best practice, we recommend that you create a .dockerignore file in the same directory as the Dockerfile. For this tutorial, your .dockerignore file should contain just one line:

target

Build an image 

Let’s build our first Docker image.

$ docker build --tag javaxin/user-service .

View local images

docker images 

REPOSITORY            TAG                 IMAGE ID            CREATED          SIZE

javaxin/user-service   latest              b1b5f29f74f0        47 minutes ago   401MB

Tag images 

An image name is made up of slash-separated name components. Name components may contain lowercase letters, digits, and separators. A separator is defined as a period, one or two underscores, or one or more dashes. A name component may not start or end with a separator.

To create a new tag for the image we’ve built above, run the following command:

$ docker tag javaxin/user-service:latest javaxin/user-service:v1.0.0

Now, run the docker images command to see a list of our local images.

$ docker images

REPOSITORY            TAG      IMAGE ID       CREATED       SIZE

javaxin/user-service   latest    bfd2fd59ae96   14 minutes ago   407MB

javaxin/user-service   v1.0.0    bfd2fd59ae96   14 minutes ago   407MB

Let’s remove the tag that we just created. To do this, we’ll use the rmi command. The rmi command stands for “remove image”.

$ docker rmi javaxin/user-service:v1.0.0

Untagged: javaxin/user-service:v1.0.0

Note that the response from Docker tells us that the image has not been removed but only “untagged”. You can check this by running the docker images command.

$ docker images

REPOSITORY           TAG     IMAGE ID        CREATED            SIZE

javaxin/user-service   latest    bfd2fd59ae96   47 minutes ago   407MB

Our image that was tagged with :v1.0.0 has been removed, but we still have the javaxin/user-service:latest tag available on our machine.

3. Run the newly built image as a container

To run an image inside a container, we use the docker run command. The docker run command requires one parameter which is the name of the image. 

$ docker run javaxin/user-service 

Let’s open a new terminal then make a GET request to the server using the curl command.

$ curl --request GET \

--url http://localhost:8080/actuator/health \

--header 'content-type: application/json'

curl: (7) Failed to connect to localhost port 8080: Connection refused

As you can see, our curl command failed because the connection to our server was refused. It means that we were not able to connect to the localhost on port 8080. 

$ docker run --publish 8080:8080 javaxin/user-service 

Now, let’s rerun the curl command from above.

$ curl --request GET \

--url http://localhost:8080/actuator/health \

--header 'content-type: application/json'

{"status":"UP"}

  Success! We were able to connect to the application running inside of our container on port 8080.

Now, press ctrl-c to stop the container.

List containers

docker ps

CONTAINER ID   IMAGE            COMMAND                  CREATED              STATUS              PORTS                    NAMES

5ff83001608c   javaxin/user-service      "./mvnw spring-boot:…"   About a minute ago   Up About a minute   0.0.0.0:8080->8080/tcp   trusting_beaver

Run in detached mode

Docker can run your container in detached mode or in the background. To do this, we can use the --detach or -d for short. Docker starts your container as earlier, but this time, it will “detach” from the container and return you to the terminal prompt. 

$ docker run -d -p 8080:8080 javaxin/user-service 

Docker started our container in the background and printed the Container ID on the terminal. 

To name a container, we just need to pass the --name flag to the docker run command. 

$ docker run --rm -d -p 8080:8080 --name springboot-server javaxin/user-service

Docker Stop

 We need to pass the name of the container or we can use the container ID. 

$ docker stop trusting_beaver

Docker Restart

$ docker restart trusting_beaver 

To name a container, we just need to pass the --name flag to the docker run command.