Container Application Development with Java

Quick Start Guide

Introduction

Java is a famous programming language. Compiled Java code can run on any platform with a Java Virtual Machine, so it's highly portable. This HowTo describes the steps to get a Container with a Java Virtual Machine in it.

To be able to start Java applications there must be a Java Virtual Machine and a set of class libraries. In this HowTo the Oracle Java SE will be used. Due to the "Oracle Binary Code License Agreement" it's not allowed to offer an already prepared container image. Creating a container with Oracle Java is quite easy:

• Get a working container on the M3 device:
  • Either create a default container on the device
  • or install an already prepared (default) container from https://m3-container.net
• Download Java SE JDK
• Copy the needed parts of Java into the container

Install a container on an M3 device

Use the web interface of your M3 device:

• Menu "Administration -> Container":
  • Either click the magic wand to create a new container
  • or upload a container from https://m3-container.net
• Click the pencil to get to the settings of the new container
• Select a net interface to which the containers network interface should be bridged
• Enter at least an IPv4 address and its netmask
• Store the settings and activate the profile with a click on the blinking gear

Now you should be able to ping the container. It's assumed the container gets bridged to "net1" and has the IP address 192.168.1.3/24. Open a console and try:

joe@pc ~/ ping 192.168.1.3

In case this is successful the next step is to establish an SSH connection to the container as user "root" with password "root":

joe@pc ~/ ssh root@192.168.1.3

Download and install Java

Oracle offers its JRE 8 (Java Runtime Environment) precompiled for ARMv7 within the JDK (Java Development Kit)

• Navigate your browser to http://www.oracle.com/technetwork/java/javase/downloads.
• Click the Java 8 JDK download button (e.g. after "Java SE 8u144")
• Accept the "Oracle Binary Code License Agreement for Java SE"

• Download the version for Linux ARM 32 Hard Float ABI (click jdk-8-XXXX-linux-arm32-vfp-hflt.tar.gz")

• Unpack the downloaded image on your PC
  

  
  
  joe@pc ~/ tar xf jdk-8u144-linux-arm32-vfp-hflt.tar.gz 
  
  

• Enter the "jre" directory of the extracted directory:
  

  
  
  joe@pc ~/ cd jdk1.8.0_144/jre
  
  

• Transfer all files into the container on the M3 device:
  

  
  
  joe@pc ~/ scp -r * root@192.168.1.3:/
  
  

  
  Alternatively you can pack the content of this directory, transfer it to the container and extract it in its / directory.

Run your first Java application

Create a file with the name "HelloWorld.java" on your PC:

joe@pc ~/ nano HelloWorld.java

Copy and paste this Code:
Create a file with the name "HelloWorld.java" on your PC:

public class HelloWorld

{

public static void main (String[] args)

{

System.out.println("Hello World!");

}

}

Store and exit the editor. Run the Java compiler, which will create a .class file containing the program, that the java virtual machine can handle:

joe@pc ~/ javac HelloWorld.java

Transfer the binary file HelloWorld.class file into the container:

joe@pc ~/ scp HelloWorld.class root@192.168.1.3:~

Log in to your container and start the application:

joe@pc ~/ ssh root@192.168.1.3

root@container_d4273e3d ~ $ java HelloWorld

Finished!

Your Java container is ready, you can use it as a template container for future Java projects. Done!