Monday 11 July 2022

How to Create your first Docker image using Java?

 


Check post for MAVEN commands and Interview Question:
MAVEN Commands

Docker Commands:Interview Question



Though we all must know about Docker, but let’s revise a brief introduction about Docker:

Docker Introduction:

- Docker is a set of platform as a service products that use OS-level virtualization to deliver software in packages called containers. 
- The service has both free and premium tiers. 
- The software that hosts the containers is called Docker Engine. 

Docker Image

A Docker image is a file used to execute code in a Docker container. 

Docker images act as a set of instructions to build a Docker container, like a template. 

Docker images also act as the starting point when using Docker. An image is comparable to a snapshot in virtual machine (VM) environments.

Create your first image using Java

Create a simple Java application

Note

If you are running OpenJDK 9, mvn package may fail with

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project helloworld: Compilation failure: Compilation failure:
[ERROR] Source option 1.5 is no longer supported. Use 1.6 or later.
[ERROR] Target option 1.5 is no longer supported. Use 1.6 or later.

because support for Java 5 was dropped in JDK9.

You can add

  <properties>
    <maven.compiler.source>1.6</maven.compiler.source>
    <maven.compiler.target>1.6</maven.compiler.target>
  </properties>

to the generated pom.xml to target 1.6 instead. See also the Build a Docker Image for Java 9 chapter.

Create a new Java project:

mvn archetype:generate -DgroupId=org.examples.java -DartifactId=helloworld -DinteractiveMode=false

Build the project:

cd helloworld
mvn package

Run the Java class:

java -cp target/helloworld-1.0-SNAPSHOT.jar org.examples.java.App

This shows the output:

Hello World!

Let’s package this application as a Docker image.

Java Docker image


Run the OpenJDK container in an interactive manner:

docker container run -it openjdk

This will open a terminal in the container. Check the version of Java:

root@8d0af9da5258:/# java -version
openjdk version "1.8.0_141"
OpenJDK Runtime Environment (build 1.8.0_141-8u141-b15-1~deb9u1-b15)
OpenJDK 64-Bit Server VM (build 25.141-b15, mixed mode)

A different JDK version may be shown in your case.

Exit out of the container by typing exit in the container shell.


DevOps Related Posts

How to create DOCKER IMAGE from SCRATCH? Click above link for steps


Docker image repositories


Docker images get stored in private or public repositories, such as those in the Docker Hub cloud registry service, from which users can deploy containers and test and share images. Docker Hub's Docker Trusted Registry also provides image management and access control capabilities.

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Top API Interview Question 1-10

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SeleniumWebdriver Automation Testing Interview Questions:
API Testing Interview Question Set:
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https://automationreinvented.blogspot.com/2020/02/top-18-docker-commands-for-aytomation.html
 
Linux Interview question Set
https://automationreinvented.blogspot.com/search/label/Linux
 
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Java Related Interview Question Set
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Coding Interview Question Set:
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Mobile Testing Interview Question Set:
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Python Interview Question Set for QAE - SDET - SDE:
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