Use Javascript scripting engine in Java 17

Question

I have to move a project from Java 8 to Java 17.

I could solve most issues, but it contains a method, in which I use the ScriptEngineManager to evaluate a mathematical term.

 ScriptEngineManager mgr = new ScriptEngineManager();
 ScriptEngine e = mgr.getEngineByName("JavaScript");
 
 String t = "5*7";
 if (isMathTerm(t)) {
    System.out.println(e.eval(t).toString());
 }

In Java 8 it works as required, but in Java 17 e is always null.

According to google, the JavaScript Engine is no longer supported in Java 17.

Due to project constraints, I am not allowed to use third party libraries.

Is there a proper way to handle this in Java 17?

Answer 1

The Nashorn JavaScript Engine has been removed from Java. Deprecated in Java 11, removed in Java 15.

So you need to use different script engine, as GraalVM.

switch to the GraalVM JavaScript engine. First, add the required dependencies to your project.

<dependency>
  <groupId>org.graalvm.js</groupId>
  <artifactId>js</artifactId>
  <version>22.0.0</version>
</dependency>  
<dependency>
  <groupId>org.graalvm.js</groupId>
  <artifactId>js-scriptengine</artifactId>
  <version>22.0.0</version>
</dependency>

Then change the engine name to graal.js.

// Graal
ScriptEngine graalEngine = new ScriptEngineManager().getEngineByName("graal.js");
graalEngine.eval("print('Hello World!');");

You can check which engines available using

new ScriptEngineManager().getEngineFactories();

Or add different script engines to your project as velocity, jexl, groovy,...

Answer 2

Nashorn script engine is maintained as a separate standalone project now

https://github.com/openjdk/nashorn

Maven artifact from this project is available as well:

https://mvnrepository.com/artifact/org.openjdk.nashorn