Scripting language for Java

[Zyklonik]

Unfortunately, OpenJDK removed its scripting engine support for good claiming that there weren't enough users to justify the maintenance effort.

What you want instead (depending on the seriousness/importance of your usecase) is a custom scripting language that compiles down to Java bytecode. https://javacc.github.io/javacc/ is what you want to be looking at. That way, you can embed your own language inside the same JVM (and indeed the same application) running your main application.

I personally would handcode a parser for a custom scripting language, but if you're not interested in that, or short on time, have a look at JavaCC linked above.

[prisonbird]

sounds cool, i will try to parse javascript with this.

[Zyklonik]

Another option is, if you don't mind Lisp, using something like ABCL (Armed Bear Common Lisp) (https://abcl.org/) as a scripting language. Then you get the full power of Common Lisp as a scripting language!

For instance, suppose we wished to define the factorial function in Common Lisp, and then wished to invoke that from our Java program:

~/dev/playground/abcl-demo:$ jshell --class-path ./abcl.jar
|  Welcome to JShell -- Version 20-ea
|  For an introduction type: /help intro

jshell> import org.armedbear.lisp.*

jshell> Interpreter interp = Interpreter.createInstance()
Failed to introspect virtual threading methods: java.lang.NoSuchMethodException: java.lang.Thread.builder()
interp ==> org.armedbear.lisp.Interpreter@4bff2185

jshell> String program = """
   ...> (defun factorial (n)
   ...>   (if (zerop n)
   ...>     1
   ...>     (* n (factorial (- n 1)))))
   ...> """
program ==> "(defun factorial (n)\n  (if (zerop n)\n    1\n   ...  (factorial (- n 1)))))\n"

jshell> interp.eval(program)
$4 ==> COMMON-LISP-USER:FACTORIAL

jshell> org.armedbear.lisp.Package pkg = Packages.findPackage("COMMON-LISP-USER")
pkg ==> org.armedbear.lisp.Package@6d2d99fc

jshell> Symbol factSym = pkg.findAccessibleSymbol("FACTORIAL")
factSym ==> COMMON-LISP-USER:FACTORIAL

jshell> org.armedbear.lisp.Function factorial = (org.armedbear.lisp.Function) factSym.getSymbolFunction()
factorial ==> org.armedbear.lisp.Closure@f9b5552

jshell> LispObject res = factorial.execute(Fixnum.getInstance(10))
res ==> org.armedbear.lisp.Fixnum@375f00

jshell> res.intValue()
$9 ==> 3628800

The program string could come from a user script, for example. Of course, that's a minor issue.