Cannot find Java System compiler during compilation of jpa classes///Error while generating model

Question

The first error message appears when I try to generate the "Business Model":

    Error while generating model

                Generic error

I have this message in the file "knowageMeta.log".

    01 ago 2020 22:32:13,603 ERROR it.eng.knowage.meta.generator.utils.Compiler.compile:125 - Cannot find Java System compiler     during compilation of jpa classes, check if JDK is correctly installed.
    01 ago 2020 22:32:13,624 ERROR it.eng.knowage.meta.service.MetaService.buildModel:793 - Error during metamodel generation       :java.lang.NullPointerException

I have set the following environment variables:

    echo $JAVA_HOME 

         /usr/lib/jvm/java-8-openjdk-amd64

    echo $JAVA_HOME
        /usr/lib/jvm/java-8-openjdk-amd64

    echo $PATH

        /usr/lib/jvm/java-8-openjdk-amd64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

I run the script "./knowage_startup.sh" from the user "root"

I would appreciate your support to continue moving forward.

Thank you so much,

Comments

This tipically happens when a JRE is detected instead of a JDK. Is there any JRE_HOME defined?

---

It is certainly what I saw in all the documentation and in other answers here. Now this value:

         echo $JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64

I put the JRE_HOME this value to test: 

    echo $JRE_HOME
        /usr/lib/jvm/java-8-openjdk-amd64/jre

and I keep getting the same error.

I even put all the .sh files in the beginning lines  the following:

      # Ernesto

     export JRE_HOME = / usr / lib / jvm / java-8-openjdk-amd64 

     export JAVA_HOME = / usr / lib / jvm / java-8-openjdk-amd64

     ###### 

for each file:

          /home/econtreras/RMS40/Knowage-Server-CE/bin/catalina.sh    

     /home/econtreras/RMS40/Knowage-Server-CE/bin/daemon.sh 

        /home/econtreras/RMS40/Knowage-Server-CE/bin/digest.sh 

       /home/econtreras/RMS40/Knowage-Server-CE/bin/knowage_shutdown.sh 

       /home/econtreras/RMS40/Knowage-Server-CE/bin/knowage_startup.sh 

      /home/econtreras/RMS40/Knowage-Server-CE/bin/setclasspath.sh 

       /home/econtreras/RMS40/Knowage-Server-CE/bin/setenv.sh 

       /home/econtreras/RMS40/Knowage-Server-CE/bin/tool-wrapper.sh

But nothing,

I would really appreciate your support

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JRE is not enough, you must have a valid JDK. In case both JAVA_HOME and JRE_HOME are defined, JRE_HOME wins, therefore you should remove the JRE_HOME variable.

---

Certainly I did not have a valid JDK, although I assumed that I had installed it. 

I re-verified it with a java program: 

       System.out.println (System.getProperty ("java.home")); 

       System.out.println (ToolProvider.getSystemJavaCompiler ()); 

   The last line returned null 

I reinstalled Java 8 and the situation was solved: 

        apt-get update 

        apt-get install software-properties-common 

        apt-add-repository 'deb http://security.debian.org/debian-security stretch / updates main' 

        apt-get update apt-get install openjdk-8-jdk 

Now the java program returns: 

     System.out.println (System.getProperty ("java.home")); 

                  / usr / lib / jvm / java-8-openjdk-amd64 / jre 

    System.out.println (ToolProvider.getSystemJavaCompiler ()); 

                com.sun.tools.javac.api.JavacTool@330bedb4 

Thank you very much to all,