Runtime Java Module Generation for Game Plugins

Question

Edit: Clarification:

I want to create a named module during runtime and put dynamically loaded classes into the created module.

I am attempting to build a framework that allows for code generation that is compatible with Java 9's module system. I require the ability to load some generated byte code into a "virtual" module.

From what I can tell after looking though the Java code there are no exported and public methods that allow me to do anything like this, but I am sure I am missing something.

For an example, let's say this class is generated for the module "handler".

package handler;

public class ModHandler{
    public static String fireEvent(){
        return "This is a string from the generated module!";
    }
}

How do I make the "handler" module and load the bytecode into it? How would you add exports and requires into the module? I do not want to write anything to the disk to implement this.

Answer 1

You have to create a ModuleLayer from a Configuration. This requires a Set of Paths to pass to a ModuleFinder instance that can be created with ModuleFinder.of.

This example lists the jars in plugins and loads the modules.

// List all jar files in ./plugins
File[] pluginFiles = new File("plugins").listFiles((f,n)->n.endsWith(".jar"));
// Convert to Paths
Arrays.stream(pluginFiles).map(File::toPath).collect(Collectors.toSet());
// Create a module finder from those jars
ModuleFinder finder = ModuleFinder.of(Set.of(pluginFiles));
// Get the boot config
Configuration parentConfig = ModuleLayer.boot().configuration();
// Create a new configuration
Configuration configuration = parentConfig.resolve(
    finder,
    ModuleFinder.of(),
    // This gets the names of all the modules and tells the Config to load them
    finder.findAll().stream().map(mr->mr.descriptor().name()).collect(Collectors.toList())
);
// Create the ModuleLayer, you can now interact with the modules
ModuleLayer layer = ModuleLayer.boot().defineModulesWithOneLoader(configuration, ClassLoader.getSystemClassLoader());

This was so much harder to find than one might think, with this you can create a custom ModuleFinder and do weird and wonderful things.