Developing on a remote PC

GITHUB PROJECT: https://github.com/Pi4J/pi4j-maven-archetype

Developing Java Programs Using a Remote PC Workstation

Writing your Java program, compiling and running it directly on the Raspberry Pi board as shown in the previous chapter is perfectly fine, of course, but there is an alternative way to arrange your developing laboratory, using a normal desktop computer as Remote Developing Workstation (RDW).

This Maven Archetype will give you a tool to generate Pi4J V.2 skeleton Java projects. You can use it for your next Pi4j project and you will be able to develop your program on the remote workstation (RDW), compile them, transmit the executable code on the target Pi board and run it. You can also start a remote debugging session.

There are some pros. and cons. in such a developing arrangement:

  • Pros:
    • Your RDW has much more resources like memory, disk capacity and CPU power than a Raspberry Pi, and this is true for a P4 model too. You can store all your programs in the desktop computer.
    • You do not have to install on the Raspberry Pi the Visual Studio Code (or your preferred IDE program), the Java JDK (JRE it is enough), Maven and the other development tools. You do not need to connect the screen, the keyboard and the mouse to the Raspberry Pi
    • You can use smaller PI models
  • Cons:
    • You can’t run Web applications (using a web container like Tomcat or similar)

Setting Up

Configure the RPi for Headless mode

The Headless Mode configuration enables the RPi board to communicate with the RDW over SSH protocol.

These are the needed steps:

  • Check if the RDW is equipped with a SSH Client. If the RDW OS is Linux you already have it
  • For Windows you can use putty, MobaXterm or you can enable the (new) OpenSsh Client porting on Windows 10
  • Connect both the RPi and RDW to your local network
  • Follow this guide to configure your RPi
  • Install the Maven tool on the RDW

You should now be able to open a SSH Terminal window on RDW and to remotely login on the RPi board.

Install the pi4j-maven-archetype

Goto the Github Pi4J Maven Archetype repository and download the project clicking on the green Code button and selecting Download ZIP

  • Unzip the archetype file in a FOLDER
  • cd FOLDER/pi4j-maven-archetype-main
  • mvn install

Congratulation ! - Now you are ready to generate your first Project Template

Generate a new Project Template

Let suppose you want to begin the new wonderful PI4J V.2 project my-project, to do this follow these steps:

  • mkdir my-project
  • cd my-project
  • mvn archetype:generate -DarchetypeCatalog=local
  • answer to the questions the archetype asks you (see below for details)

Configuring Your New Project

Before starting the new project generation, the archetype asks some configuration data. The list of question and the replies are shown here below:

  1. Choose archetype: select the pi4j-maven-archetype from the list proposed
  2. Define value for property ‘groupId’: choose the Maven groupId for your project. (If don’t know what is a groupId, don’t worry, just type “com.example” for now)
  3. Define value for property ‘artifactId’: choose a name for the program executable your project will produce
  4. Define value for property ‘version’: 1.0-SNAPSHOT: type Enter to accept the default value shown, or type the initial program version, something like 1.0.0
  5. Define value for property ‘package’: com.example: type Enter to accept the default value shown

The archetype now shows you a summary of the configuration parameters you have just typed in, plus the values proposed for the main-class and package parameters. If the list is ok for you, reply Y to accept, otherwise reply N to change one or more values (you will have to re-type all parameter values …)

After the list confirmation, the archetype generates a new maven project template for you.

Congratulations

You should be able to open the new project with your preferred java IDE. The IDE should be able to recognize the project as a valid Maven project.

Note on the Java Runtime

If you are not using the default Raspberry Pi OS full edition and/or included Java, you may get this kind of error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-antrun-plugin:3.0.0:run (exec) on project ...: An Ant BuildException has occured: The following error occurred while executing this line:
[ERROR] ...\antrun\build.xml:166: The following error occurred while executing this line:
[ERROR] ...\antrun\build.xml:123: Remote command failed with exit status 1
[ERROR] around Ant part ...... @ 9:59 in ...\antrun\build-main.xml

This can be caused by a mis-configured Java runtime. The default value in raspberry.properties is:

target.remote.jre=/usr/lib/jvm/default-java

Check if this value exists and links to your Java runtime, or find the location of your installed JDK with sudo find / -iname java and use the result in your configuration.

For instance: a Raspberry Pi Zero (type 1) with ARMv6 requires a specific Java version for this type of processor. This is described more in detail on “Java for ARMv6/7/8”. If you use Azul Zulu JDK, you will need to change the configuration to:

target.remote.jre=/usr/lib/jvm/zulu11.41.75-ca-jdk11.0.8-linux_aarch32hf

Explore the New Project Template

Feel free to explore the new project familiarizing with the folder structure. These are the most important features:

  • The file README.md contains the intruction to configure the connection(s) to your RPi board(s) and the decription of the Maven commands to build your project, transfer the executable code to the target RPi, run it and also open a debugger session.
  • The pom.xml file already includes the dependencies needed to compile your program with the Pi4J V.2 libraries.
  • The platform folder contains an example configuration file for connecting to you RPi board. Read the README.md explanation, open the platform/raspberry.properties file (or copy it to a new file) and edit it to describe how to connect to your RPi

Thanks to Adi and Luca Buraggi for this contribution.