Running javafx sample on JDK 11 with OpenJFX 11 JMODS on Module Path

Question

I have downloaded the JavaFX Jmod files from OpenJFX project and placed them in the directory G:\openjfx\javafx-jmods-11. I am using OpenJDK 11 which has no JavaFX jmod in JAVA_HOME/jmods i.e it doesn't come with JavaFX distribution.

Module info file:

module gui{
    requires javafx.graphics;
    requires javafx.controls;

    exports com.test;
}

I compile with following:

javac -p G:\openjfx\javafx-jmods-11 -d mods --module-source-path src 
    src\gui\com\test\*.java src\gui\module-info.java

Compilation succeeds. But I am unable to run the compiled code using the below command:

java -p G:\openjfx\javafx-jmods-11;mods -m gui/com.test.CreateGuiDemo

But I get the below error:

Error occurred during initialization of boot layer
java.lang.module.FindException: Module javafx.graphics not found, required by gui

Answer 1

I believe there is an explanation for the error you are facing: jmods can't be used at run time.

This is explained here: http://openjdk.java.net/jeps/261#Packaging:-JMOD-files:

JMOD files can be used at compile time and link time, but not at run time. To support them at run time would require, in general, that we be prepared to extract and link native-code libraries on-the-fly.

and credit goes to this answer.

So I've done some simple module hellofx:

module hellofx {
    requires javafx.controls;

    exports hellofx;
}

with the HelloFX sample from here and downloaded the jmods for JavaFX 11 for my platform from here. I've also downloaded the JavaFX 11 SDK (jars) from the same location.

Compile time

At compile time, we can do, with jmods:

javac -p /path-to/javafx-jmods-11/ -d mods/hellofx $(find src/hellofx -name "*.java")

or with SDK:

javac -p /path-to/javafx-sdk-11/lib -d mods/hellofx $(find src/hellofx -name "*.java")    

In both cases, the result is exactly the same, as expected: Native libraries are not required during compile time.

Run time

Now we want to run our little module.

With jmods, as stated by the OP, running:

java -p /path-to/javafx-jmods-11/:mods -m hellofx/hellofx.HelloFX   

fails with:

Error occurred during initialization of boot layer
  java.lang.module.FindException: Module javafx.controls not found, required by hellofx

But using the SDK, works:

java -p /path-to/javafx-sdk-11/lib/:mods -m hellofx/hellofx.HelloFX

Link time

As stated by the JEP-261, jmods work as well at link time, so we can use the jlink tool in between compile time and run time.

You can use the jlink tool to assemble and optimize a set of modules and their dependencies into a custom runtime image. (source)

So let's do:

jlink -p /path-to/javafx-jmods-11/:mods --add-modules=hellofx --output links

that will generate a folder with 90.7 MB (on my Mac). Note that the lib folder contains all the required native libraries from Java 11 and from JavaFX 11, as well as a 70.5 MB file named modules.

Run time (2)

And we can finally do:

links/bin/java -m hellofx/hellofx.HelloFX

And that will work.

In conclusion, if we want to use only jmods for compiling and running our modules, we need to give an extra step with jlink. Otherwise, for runtime we'll need the JavaFX SDK.