How to get Graal SDK packages to work without Maven?

Question

I am developing a Java application that needs to execute JavaScript. Nashorn JS engine is about to get deprecated and the replacement is the set of APIs provided by Graal SDK which makes use of GraalVM. The virtual machine that essentially executes a number of languages.

At least that is what I think. So I spent a day trying to get it working. I downloaded GraalVM rc6 that uses JDK 8. I use IntelliJ IDEA and I added GraalVM as a new JDK. I found it strange that I am supposed to add a virtual machine as a development kit, but I knew it is based on JDK 8 so I was ok with it.

And the problem was unlike others, I could not get the new packages to work. My IDE told me it cannot resolve them.

Actually, none of the org.graalvm packages could be resolved.

So I downloaded JDK 11 build 28 because as far as I know JDK 11 comes with GraalVM since build 20.

Actually, in this case, some of the packages could be found, but far less than expected: for instance org.graalvm.polyglot still could not be resolved.

Finally, I tried adding Graal SDK from Maven and the packages were resolved. Now I get an exception when running:

Context ctx = Context.create(“js”);

No language and polyglot implementation were found on the classpath. Make sure the truffle-api.jar is on the classpath.

I thought the problem in the first 2 cases was actually not acquiring GraalVM JDK, but it throws the exception even this way.

Can someone experienced explain the matter?

Answer 1

IntelliJ is not adding all of the Jars from the Graal SDK to your classpath.

You can add the Jars to your classpath inside IntelliJ by navigating to

File > Project Structure > SDKs > Choose your Graal SDK

Then click the + button at the bottom to add the Jar files. Adding the graal-sdk.jar will fix the problem with finding the org.graalvm package.

This will avoid having to modify your pom.xml file to fix a problem with the IDE.

Answer 2

GraalVM

GraalVM is a high-performance embeddable polyglot virtual machine currently supporting a number of programming languages: Java (and JVM languages), JavaScript (including node.js), Ruby, R, Python, and C/C++ and other languages with the LLVM backend.

You can download the pre-built distribution of GraalVM here: https://www.graalvm.org/downloads. Among other things it includes a java runtime, a node runtime, a JavaScript engine called Graal.js, etc.

Graal SDK is the polyglot API allowing GraalVM to work with all the language implementations it can run. This polyglot API is packaged as a jar file: $GRAALVM_HOME/jre/lib/boot/graal-sdk.jar.

Adding that file as an external library to your IDEA project / module, would allow the IDE to find the classes like: org.graalvm.polyglot.Context and org.graalvm.polyglot.Value which are necessary to interop with the languages, including the JavaScript implementation.

If your project is using Maven, you can add a system dependency on that file, and maven will find it on any system where $JAVA_HOME is set to point at a GraalVM distribution.

<dependency>
    <groupId>org.graalvm</groupId>
    <artifactId>graal-sdk</artifactId>
    <version>1.0.0-rc</version>
    <scope>system</scope>
    <systemPath>${java.home}/lib/boot/graal-sdk.jar</systemPath>
</dependency>

Now when you will run the java command from the GraalVM distribution, the necessary files will be added to the classpath automatically. So nothing more is necessary to run something like the following in the IDE:

import org.graalvm.polyglot.*;
public class Main {
    public static void main(String[] args) {
        Context polyglot = Context.create();
        Value array = polyglot.eval("js", "[1,2,42,4]");
        System.out.println(array.getArrayElement(2).asInt());
    }
}

Now this is because GraalVM has the Graal.js JavaScript engine enabled by default.

If you want to run it on a stock JDK you need to add more things to the classpath.

Running Graal.js on a stock JDK**

There's this question on how to run Graal.js on the stock JDK: How to use graaljs ? Is there a place where to get a .jar file/files?. The accepted answer tells in more details where to find the necessary jar files to make it work on Java 8.

In a nutshell you need to add the following jar files to the classpath to make it actually run:

• graal-sdk.jar - GraalVM polyglot API
• truffle-api.jar - API for language implementations.
• graaljs.jar - this is the implementation of GraalVM's JavaScript Engine
• graaljs-scriptengine.jar -- allows to use Graal.js through the Java script engine API.
• graaljs-launcher.jar
• tregex.jar -- regexp library
• truffle-profiler.jar - profiler for Truffle languages implementations
• chromeinspector.jar - debugger integration
• launcher-common.jar

You can find them in the GraalVM distribution that you downloaded, both editions would work fine.

Now without the Graal compiler the performance of the JavaScript engine would not be optimal. As you mentioned yourself JDK 11 comes with a snapshot of the Graal compiler (not GraalVM, which is a full distribution of the GraalVM project including JS engine, LLVM bitcode interpreter, node implementation, JVM, etc). You can enable the Graal compiler by passing --XX:+UnlockExperimentalVMOptions --XX:+UseJVMCICompiler to the java command.

Now running it all on JDK 11 might not work because JDK 11 is sufficiently different from JDK 8 and there could be problems with the module system or things missing (like jax-b), but it also might work. It would work on JDK 8.