How can I continue to use Javascript in Java 15 onwards

Question

In my Java application a small put important feature is to be able to rename audio files based on their metadata (e.g album/artist -title) and the mask is specified using Javascript, this makes for a very flexible and powerful renaming feature.

I knew Javascript was being deprecated but it now seems it is actually going to be removed from Java 15 onwards. This loss of functionality could be a major problem for me so I ask even if it is officially removed is there a way I can continue to use Javascript within a Java 15 application, i.e will it be available as an opensrc plugin that I can use at my own risk. The fact that development has stopped at Ecmascript 5.1 is not a major issue for me.

There was mention of using GraalVM but without explanation how to do this and I don't see that fits in with my scenario, specifically my application is available on some 32bit Arm environments and GraalVM is not available for 32bit.

I have already moved from Java 11 to Java 14 to resolve some other issues, so I cannot really go back to Java 11, and since Java 14 is not a LTS release I cannot really stick with Java 14 over long period of time.

This is the bulk of my Javascript code

try
{
    mask = includeUserDefinedFunctions(mask);
    ScriptEngine engine = manager.getEngineByName("JavaScript");
    for(SongFieldName next:SongFieldName.values())
    {
        if(next.getScriptVar()!=null && next.getSongFieldKey()!=null)
        {  
            engine.put(next.getScriptVar(), cleanValue(song.getFieldValueSpaceSeparatedOrEmptyString(next.getSongFieldKey()), song));
        }
    }
    String result = (String)engine.eval(mask);
    return result;
}
catch(ScriptException se)
{
    throw se;
}

Answer 1

You can run GraalVM's JavaScript Engine on any JVM as a bunch of dependencies pulled from Maven central. Here's an example: https://github.com/graalvm/graaljs/blob/master/docs/user/RunOnJDK.md

It will be slower without the GraalVM compiler, because the language implementation framework for GraalVM needs certain api from the compiler which afaik is not in other JITs.

If you will look into migrating your application to use GraalVM's JavaScript, if you use certain Nashorn features it might not work out of the code, consider starting with the --nashorn-compatibility-mode (here are more details about it: https://github.com/graalvm/graaljs/blob/master/docs/user/NashornMigrationGuide.md).

Answer 2

You can use a standalone version of Nashorn: https://github.com/openjdk/nashorn.

Nashorn is a JPMS module, so make sure it and its transitive dependencies (Nashorn depends on several ASM JARs) are on your application's module path, or appropriately added to a module layer, or otherwise configured as modules.

While standalone Nashorn is primarily meant to be used with Java 15 and later versions, it can also be used with Java versions 11 to 14 that have a built-in version of Nashorn too. See this page for details on use when both versions are present.