gradle Jigsaw module not found

Question

I try to run a very simple gradle project which uses java 9 modules, but i receive the following error.

/home/vadim/IdeaProjects/test_modules/src/main/java/mo         


        

Answer 1

Unfortunately, gradle does not treat every jar as a module (in simple words). If you want to find out how exactly is gradle building the module-path (as opposed to class-path), you probably want to start from here, specifically at the isModuleJar method. It's pretty easy to understand (though it took me almost two days to set-up gradle and debug the problem out) that the dependency that you are trying to use : gradle says that it is not a module (it isn't wrong, but I am not sure it is correct either). To make it very correct, gradle will add your dependency to the CLASSPATH, but in the very next line: it will not add your dependency to the module-path, because if fails the filter in isModuleJar.

I do not know if this is a bug or not, or may be this is on purpose, but the solution is easy:

plugins.withType(JavaPlugin).configureEach {
   java {
       modularity.inferModulePath = true
   }

   tasks.withType(JavaCompile) {
      doFirst {
          options.compilerArgs = [
                 '--module-path', classpath.asPath,
          ]
          classpath = files()
    }
}

you add it to the path, on purpose. I will flag this as a defect and let's see what they have to say.

EDIT

Even better, use a plugin that is written by a gradle commiter:

plugins {
    id 'java'
    id 'de.jjohannes.extra-java-module-info' version "0.1"
}

And the easiest option on your case is to do :

extraJavaModuleInfo {
     automaticModule("HdrHistogram-2.1.12.jar", "HdrHistogram")
}