pi4j-example-javafx returns UnsupportedOperationException: Unable to open DISPLAY

[bduitp]

Hi,
First of all i would like to thank all developers and maintainers to bring the wonders of Rpi to Java!
But now i have a very annoying issue:
Context:
Rpi 3B+ / Ubuntu for rpi ( with user interface, so not headless) - development on linux desktop (Ubuntu 20.04.4LTS).
Goal: developing a prototype for a control to distribute biscuits on a conveyerbelt following certain businessrules. Therefor i need to combine the user interface capabilities of javafx but at the same time i need access to the gpio's. I broke my code into two parts: The "interface" part with javafx and opencv for java (to capture images) and a second part which controls a vibration motor and some led's. Each part works as expected, with that important note: the javafx part is run as user "pi" and the gpio controlling part has to be run as "root" (well, in "sudo" mode).
I want to combine these two parts in 1 application so i ran into the permissions discrepancy. I found no way to run Ubuntu on rpi as root (and i mean running the whole gui as root - yes i know, this is not recommended anyway) and there is no way to run Pi4J as a non-root user.
BTW: the error i get is "UnsupportedOperationException: Unable to open DISPLAY" if i try to run the application in sudo mode. The "DISPLAY" is not known for user "root"
So, googeling learned me that there was a pi4j-example-javafx. So i meticulously followed the instructions to run that example and, guess what: i ran into the same problem with the same error.
Hereafter i'll put the full stack trace. What am i doing wrong? What am i missing? Any input would be very welcome!
Bart Devos

sudo ./run.sh No protocol specified Exception in thread "main" java.lang.reflect.InvocationTargetException at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:567) at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051) Caused by: java.lang.UnsupportedOperationException: Unable to open DISPLAY at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.lambda$new$6(GtkApplication.java:173) at java.base/java.security.AccessController.doPrivileged(AccessController.java:312) at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.<init>(GtkApplication.java:171) at javafx.graphics/com.sun.glass.ui.gtk.GtkPlatformFactory.createApplication(GtkPlatformFactory.java:41) at javafx.graphics/com.sun.glass.ui.Application.run(Application.java:144) at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:280) at javafx.graphics/com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:269) at javafx.graphics/com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:158) at javafx.graphics/com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:658) at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:409) at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363) ... 5 more

[FDelporte]

Hi Bart, not sure if this will a real answer to your question, but can you also take a look at https://github.com/Pi4J/pi4j-template-javafx. This was created by Dieter Holz and seems as a perfect introduction to what you want to achieve with separated business logic and UI.

Regarding the DISPLAY-issue, maybe there is some valuable info here https://unix.stackexchange.com/questions/241394/ssh-and-sudo-but-no-display

[bduitp]

Thank you Frank for your immediate response!
Meanwhile i found a solution myself (apparently writing down the problem gives some enlightenment...;-), but i will investigate your links if these are better (or more secure) solutions.
This is how i could get it work for now (this is part of a ant script to build and run remote):
<target name="run-jar-remote" depends="copy-jar-remote"> <echo>">>> Starting ${raspberrypi}:${raspberryfolder}/${jar.filename} in run mode"</echo> <sshexec host="${raspberrypi}" username="${username}" password="${password}" trust="true" failonerror="true" usepty="true" command="export DISPLAY=:0; xhost [email protected]; sudo java -Djava.library.path=/home/pi/lib/opencv-4.5.5/build/lib/ -jar ${appname}/${jar.filename}" /> <echo>">>> Running app in runmode done..."</echo> </target>
Thanks again for your effort!
Bart.

[FDelporte]

That's how it always works... writing it down reveals the issue ;-)
BTW "biscuits on a conveyerbelt" calls for pictures, movies, and description for https://pi4j.com/featured-projects/

[bduitp]

First of all i 'll have to succeed in what i want to achieve... But promised!