Pi4j to use java with raspberry Pi not working

Question

I am honestly about to just give up, i've tried so many different possibilities, for multiple weeks now, almost a month, of multiple problems.

I am a new-ish programmer, especially with java, but i have a good understanding about java

I am able to create a maven project no problem, i have no problems with the structure of java itself, but i don't fully understand the pom.xml.

The file compiles just fine, but when i go to start it with java -jar (filename), i get the following output;

Exception in thread "main" java.lang.NoClassDefFoundError: com/pi4j/Pi4J at com.pi.rasberri.Main.main(Main.java:16) Caused by: java.lang.ClassNotFoundException: com.pi4j.Pi4J at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520) ... 1 more

Heres my pom that i have figuratively almost dismembered;

   (The long links)
<modelVersion>4.0.0</modelVersion>
<groupId>com.pi</groupId>
<artifactId>Rasberri</artifactId>
<version>3.6.1</version>
<packaging>jar</packaging>
<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>11</maven.compiler.source>
    <maven.compiler.target>11</maven.compiler.target>
</properties>  <dependencies>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-simple</artifactId>
        <version>1.7.32</version>
    </dependency>
    <dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.32</version>
    </dependency>
    <dependency>
        <groupId>com.pi4j</groupId>
        <artifactId>pi4j-core</artifactId>
        <version>2.0</version>
    </dependency>
    <dependency>
    <groupId>com.pi4j</groupId>
    <artifactId>pi4j-plugin-raspberrypi</artifactId>
    <version>2.0</version>
</dependency>
<dependency>
    <groupId>com.pi4j</groupId>
    <artifactId>pi4j-plugin-pigpio</artifactId>
    <version>2.0</version>
</dependency>
</dependencies> <build>
  <plugins>
      <plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2</version> </plugin>    <plugin>    <groupId>org.apache.maven.plugins</groupId>

maven-jar-plugin 3.1.0 true com.pi.rasberri.Main lib/ true true com.pi.rasberri.Main false true

And my code, which is com.pi.rasberri.Main

    package com.pi.rasberri;

import com.pi4j.Pi4J;
import com.pi4j.io.gpio.digital.DigitalOutput;
import com.pi4j.io.gpio.digital.DigitalState;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Main {
   
    private static final int PIN_LED = 6;
    
    public static void main(String[] args) throws Exception{
        
       var pi4j = Pi4J.newAutoContext();
        int x = 0;
        
        var ledConfig = DigitalOutput.newConfigBuilder(pi4j)
           .id("led")
           .name("LED Flasher")
           .address(PIN_LED)
           .shutdown(DigitalState.LOW)
           .initial(DigitalState.LOW)
           .provider("pigpio-digital-output");
      
        var led = pi4j.create(ledConfig);
        
        
        while(x != 5){
        
            led.high();
            sleep(1000);
            led.low();
            sleep(500);
            x++;
        }
    }
    
    static void sleep(int z){
    
        try {
           Thread.sleep(z);
        }   catch (InterruptedException ex) {
           System.out.println("Thread.sleep went fucky wucky");
        }
    }
    }

I would appreciate anything that can even direct me somewhere, because i am quite lost at this point, and of course, if i figure out the answer, i will let everyone know! Thanks in advance

                       **UPDATE**
Thank you, tgdavies, the article you linked https://stackoverflow.com/a/574650/17644313 was the answer to that specific problem!**

Just in case anyone else has the same chain of issues as me;

But with that being said, i ran directly into another error;

[main] INFO com.pi4j.Pi4J - New auto context [main] INFO com.pi4j.Pi4J - New context builder [main] INFO com.pi4j.platform.impl.DefaultRuntimePlatforms - adding platform to managed platform map [id=raspberrypi; name=RaspberryPi Platform; priority=5; class=com.pi4j.plugin.raspberrypi.platform.RaspberryPiPlatform] Exception in thread "main" com.pi4j.provider.exception.ProviderNotFoundException: Pi4J provider [pigpio-digital-output] could not be found. Please include this 'provider' JAR in the classpath. at com.pi4j.provider.impl.DefaultRuntimeProviders.get(DefaultRuntimeProviders.java:238) at com.pi4j.provider.impl.DefaultProviders.get(DefaultProviders.java:147) at com.pi4j.provider.Providers.get(Providers.java:253) at com.pi4j.context.Context.create(Context.java:316) at com.pi4j.internal.IOCreator.create(IOCreator.java:58) at com.pi4j.internal.IOCreator.create(IOCreator.java:96) at com.pi4j.internal.IOCreator.create(IOCreator.java:176) at com.pi.rasberri.Main.main(Main.java:27)

I cleaned the pom.xml a littlebit;

<dependencies>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-simple</artifactId>
        <version>1.7.32</version>
    </dependency>
    <dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.32</version>
    <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>com.pi4j</groupId>
        <artifactId>pi4j-core</artifactId>
        <version>2.0</version>
    </dependency>
    <dependency>
    <groupId>com.pi4j</groupId>
    <artifactId>pi4j-plugin-raspberrypi</artifactId>
    <version>2.0</version>
</dependency>
<dependency>
    <groupId>com.pi4j</groupId>
    <artifactId>pi4j-plugin-pigpio</artifactId>
    <version>2.0</version>
</dependency>
</dependencies>
  

<build>
      <plugins>  <!--Package all libraries classes into one runnable jar -->
        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <executions>
              <execution>
                <phase>package</phase>
                <goals>
                  <goal>single</goal>
                </goals>
              </execution>
            </executions>
            <configuration>
                <archive>
                    <manifest>
                <mainClass>com.pi.rasberri.Main</mainClass>
                    </manifest>
                </archive>
              <descriptorRefs>
                <descriptorRef>jar-with-dependencies</descriptorRef>
              </descriptorRefs>
            </configuration>
        </plugin>    
</plugins>
</build>
</project>

At this point, i know of atleast 2 possibilities,

The code just needs to be run on the raspberry pi
I have entered the classpaths incorrectly

But i honestly dont really know as to where to start troubleshooting I've tried a few things, one of which being to try another method of compiling the files, but the other method just resulted in a even longer string of errors.

What should i try next? Thanks in advance! And thanks to anyone who has suggested troubleshooting steps thus far!

Oh, and the target is to hopefully just create a singular jar file to execute on the raspberry pi

update

I tried to run it on the Raspberri pi, and it resulted in the same error so it's not that

You need to have the jar in your classpath when running your code. — Thorbjørn Ravn Andersen, Dec 18 '21 at 01:01
Does this answer your question? [How can I create an executable JAR with dependencies using Maven?](https://stackoverflow.com/questions/574594/how-can-i-create-an-executable-jar-with-dependencies-using-maven) — tgdavies, Dec 18 '21 at 02:25
You have to make sure that when you "build" a maven project, you're also including the dependencies as part of the end product, for [example](https://stackoverflow.com/questions/24028921/in-maven-my-dependencies-are-set-up-but-i-get-a-classnotfoundexception-when-i-r/24030042#24030042), [example](https://stackoverflow.com/questions/24899985/this-project-cannot-be-added-because-it-does-not-produce-a-jar-file-using-an-ant/24900260#24900260) — MadProgrammer, Dec 18 '21 at 02:34
Or you could make use of a "fat jar", for [example](http://tutorials.jenkov.com/maven/maven-build-fat-jar.html), [example](https://stackoverflow.com/questions/16222748/building-a-fat-jar-using-maven). As always, you'll need to do some research into Maven to verify all the properties, been awhile since I used Maven — MadProgrammer, Dec 18 '21 at 02:34
Easiest would be to create an executable jar via maven-shade-plugin or maven-assembly-plugin to have all the dependencies available during execution... — khmarbaise, Dec 18 '21 at 11:01
Thanks tgdavies, MadProgrammer, and khmarbaise for the answers, the fix was to create a fat jar, but with that i stumble into another issue, which i have now listed in the original post — Brosbud, Dec 18 '21 at 13:13
Note that you could have saved yourself quite a bit of effort by investigating what the reported `NoClassDefFoundError` exception actually means. — Thorbjørn Ravn Andersen, Dec 19 '21 at 11:02

Brosbud · Accepted Answer · 2022-05-06T12:49:12.667

1

Thanks tgdavies, MadProgrammer, and khmarbaise for the answers, the fix was to create a fat jar, which is basically a jar file that contains all the dependencies in one file, example can be found in the original question/comments

UPDATE!!

Pi4j has posted instructions for the V2 fat jar on their website! I tried it and it works perfectly now

https://pi4j.com/getting-started/minimal-example-application-fatjar/

edited May 06 '22 at 12:49

answered Dec 18 '21 at 13:11

Brosbud

21
7

This is typically because it needs a native library and the system linker responsible for loading native libraries doesn't know how to load a zip file entry, but needs a plain file. – Thorbjørn Ravn Andersen Dec 19 '21 at 11:01
A fat jar example has recently been added to the Pi4J documentation website, see https://pi4j.com/documentation/building/fat-jar/ – Frank Feb 22 '22 at 08:42

score 1 · Answer 2 · answered Dec 18 '21 at 21:45

I do not have a Raspberry Pi to do final testing but I think I found a work-around.

Using this answer I managed to get 2021-10-30-raspios-bullseye-armhf-lite.img running in Docker. I built a project using your code and copied all files needed and tried to start it (mypiapp is my jar containing your main-class):

java -cp mypiapp-0.0.1-SNAPSHOT.jar:lib/pi4j-core-2.1.1.jar:lib/pi4j-library-pigpio-2.1.1.jar:lib/pi4j-plugin-pigpio-2.1.1.jar:lib/pi4j-plugin-raspberrypi-2.1.1.jar:lib/slf4j-api-1.7.32.jar:lib/slf4j-simple-1.7.32.jar com.github.fwi.mypiapp.MyPiApp

which then gave me the error:

[main] ERROR com.pi4j.library.pigpio.util.NativeLibraryLoader - Unable to load [libpi4j-pigpio.so] using path: [/lib/armhf/libpi4j-pigpio.so]
java.lang.UnsatisfiedLinkError: /tmp/libpi4j-pigpio1770932771276400506.so: libpigpio.so.1: cannot open shared object file: No such file or directory

which is a bummer. But at least there was no ProviderNotFoundException (which I also could reproduce using the "fat jar with dependencies"). The long java-command appears to prevent that exception from happening.

And I could improve the situation somewhat by running (in Raspbian)

apt install pigpio

and now the long java-command shows:

[main] WARN com.pi4j.library.pigpio.impl.PiGpioNativeImpl - PIGPIO ERROR: PI_INIT_FAILED; pigpio initialisation failed

which is to be expected when running in a Docker container. But at least the native library was found and loaded.

Now for the work-around which might solve the "fat jar" problems. We are gonna borrow some Maven setup and code from Spring. Spring can also build fat-jars and does it a bit more complicated but also better. The pom now looks like (update where needed with your project names):

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.1</version>
    </parent>
    
    <groupId>com.github.fwi</groupId>
    <artifactId>mypiapp</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <java.version>11</java.version>
        <start.class>com.github.fwi.mypiapp.MyPiApp</start.class>
        <pi4j.version>2.1.1</pi4j.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>com.pi4j</groupId>
            <artifactId>pi4j-plugin-raspberrypi</artifactId>
            <version>${pi4j.version}</version>
        </dependency>
        <dependency>
            <groupId>com.pi4j</groupId>
            <artifactId>pi4j-plugin-pigpio</artifactId>
            <version>${pi4j.version}</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <mainClass>${start.class}</mainClass>
                    <layout>ZIP</layout>
                    <executable>false</executable>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Simply run mvn clean package to build the fat-jar. Run it using java -jar mypiapp-fat.jar In my case, it gave the exact same error as when running with the long java-command (i.e. there was no ProviderNotFoundException). So I think this could work on a real Raspberry-Pi (the apt install pigpio might still be required though).

Some notes:

the Spring parent sets some good Maven defaults and also sets good defaults for the spring-boot-maven-plugin
Java version MUST be set using the java.version property.
update start.class with the name of the class containing your main-method.
the 3 dependencies in the pom.xml will pull in all other dependencies (dependencies of dependencies)
Spring documentation references: packaging and nested-jars launcher options.

As it appears, the reason why i couldn't make a fat jar, is that it isn't supported for pi4j v2 yet, i downgraded to 1.4 and it works fine. — Brosbud, Dec 18 '21 at 23:03

score 1 · Answer 3 · answered Feb 08 '22 at 13:23

1

I faced the same issue working with Raspberry P4, java 11 and pi4j v2. I solved it downloading pigpio library directly from the raspberry

sudo apt-get install pigpio

After the library was installed, the jar worked perfecrly. Remember also to run your program with sudo if you are not root user

answered Feb 08 '22 at 13:23

Roberto Shaba

44
5

I'll definitely try this once I find my raspberry pi again... – Brosbud Feb 21 '22 at 20:23

Pi4j to use java with raspberry Pi not working

3 Answers3