JShell has the following method:

    /**
     * Create a evaluation processing environment from which the state engine
     * and analysis support can be accessed.
     *
     * @param in Input for the running evaluation (it's System.in).
     * @param out Output for the running evaluation (it's System.out).
     * @param err Error output for the running evaluation (it's System.err).
     * @return the entry point into evaluation processing support.
     */
    public static JShell create(InputStream in, PrintStream out, PrintStream err) {
        return new JShellImpl(in, out, err);
    }

but while InputStream and PrintStream are convenient for hooking up to a Unix-like terminal window, for embedded use, it would be more convenient if it also had a method that took Readers and Writers, and so avoid the round trip from characters to bytes and back again.

-- Jon